Laminated film roll and method of producing the same

ABSTRACT

The present invention provides a new member having a low refractive index as a substitute for an air layer, for example. The laminated film roll of the present invention includes a long laminated film roll including: an ultra-low refractive index layer having a refractive index of 1.20 or less; and a resin film, wherein the ultra-low refractive index layer is stacked on the resin film. The method of forming the long laminated film roll of the present invention includes steps of: preparing a liquid containing microporous particles; coating a resin film with the liquid; and drying the liquid applied on the resin film, for example.

TECHNICAL FIELD

The present invention relates to a laminated film roll and a method ofproducing the same.

BACKGROUND ART

Disposing two substrates at a regular spacing forms an air layer whichis a void space between the substrates. The air layer formed between thesubstrates serves as a low refractive layer that reflects lightentirely, for example. Thus, for example, in the case of an opticalfilm, components such as a prism, a polarizing film, and a polarizingplate are disposed at regular spacings to provide air layers each ofwhich serves as a low refractive index layer between the components.Forming air layers in such a manner, however, requires to dispose thecomponents at regular spacings, which prevents the components from beingstacked sequentially and causes time and trouble in production.

For solving such problems, there are attempts to develop a member suchas a film having a low refractive index as a substitute for an air layerwhich is a void space between the components. As an example of such amember, which achieves a high porosity and a high strength, there aremethods of applying the member to an antireflection layer of a lens (forexample, see Patent Documents 1 to 4). In each of these methods, a layerwith void spaces (hereinafter, also referred to as a “void-providedlayer”) is formed on a lens and then baked at a high temperature of 150°C. or more for a long time. These methods, however, have the followingproblem. Since the thus obtained void-provided layer is inferior inflexibility, the layer cannot be formed on a soft resin film, which doesnot allow continuous production in the shape of a roll. On the otherhand, there is an example of application of a void-provided layer whichhas not been subjected to baking treatment (for example, see Non-PatentDocument 1). This method, however, has the following problem. Since thethus obtained void-provided layer is inferior in film strength, animpact resistance cannot be imparted, which does not allow continuousproduction in the shape of a roll.

There are also examples disclosing the method of forming a silicaaerogel film on a long resin support (for example, see Patent Documents5 and 6). These methods, however, have the following problem. Since thethus obtained void-provided layer has a refractive index of more than1.30, the layer cannot be a substitute for an air layer at all.

CITATION LIST Patent Document (s)

-   Patent Document 1: JP 2006-297329 A-   Patent Document 2: JP 2006-221144 A-   Patent Document 3: JP 2006-011175 A-   Patent Document 4: JP 2008-040171 A-   Patent Document 5: JP 2006-096019 A-   Patent Document 6: JP 2006-096967 A

Non-Patent Document(s)

-   Non-Patent Document 1: J. Mater. Chem., 2011, 21, 14830-14837

BRIEF SUMMARY OF THE INVENTION Problem to be Solved by the Invention

There has not been reported a long laminated film roll including anultra-low refractive index layer that achieves both flexibility and afilm strength and allows continuous production in the shape of a roll.Hence, the present invention is intended to provide a long laminatedfilm roll including an ultra-low refractive index layer having arefractive index of 1.20 or less, which can be a substitute for an airlayer, for example.

Means for Solving Problem

In order to achieve the above object, the present invention provides alaminated film roll including an ultra-low refractive index layer havinga refractive index of 1.20 or less; and a resin film, wherein theultra-low refractive index layer is stacked on the resin film.

The present invention also provides a laminated film including: anultra-low refractive index layer having a refractive index of 1.20 orless; and a resin film, wherein the ultra-low refractive index layer isstacked on the resin film, and in the ultra-low refractive index layer,an abrasion resistance showing a film strength, measured with BEMCOT® isin a range from 60% to 100% and a folding endurance showing flexibility,measured by an MIT test is 100 times or more.

The present invention also provides a method of producing the laminatedfilm roll according to the present invention, including steps of:preparing a liquid containing one kind or two or more kinds ofstructural units that form a structure with minute void spaces; coatinga resin film with the liquid; and drying the liquid applied on the resinfilm.

The present invention also provides an optical element including theultra-low refractive index layer of the laminated film roll or thelaminated film according to the present invention.

Effects of the Invention

The laminated film roll of the present invention having theabove-described properties achieves an ultra-low refractive index layerhaving a refractive index of 1.20 or less which can be a substitute foran air layer as well as allows continuous production in the shape of aroll, for example. Thus, there is no need to provide air layers bydisposing components at regular spacings for achieving an ultra-lowrefractive index. By disposing the ultra-low refractive index layer ofthe present invention at a desired site, an ultra-low refractive indexcan be imparted as well as a continuous production at low cost can beperformed. Thus, the laminated film roll of the present invention isvery useful to an optical element which requires an ultra-low refractiveindex, for example.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process cross sectional view schematically showing anexample of the method of forming an ultra-low refractive index layer 20on a resin film 10 in the present invention.

FIG. 2 is an illustration schematically showing an example of a part ofthe process of producing a laminated film roll of the present inventionand an example of the apparatus used therefor.

FIG. 3 is an illustration schematically showing another example of apart of the process of producing a laminated film roll of the presentinvention and another example of the apparatus used therefor.

FIG. 4 is a process cross sectional view schematically showing anotherexample of the method of forming an ultra-low refractive index layer ona base in the present invention.

FIG. 5 is an illustration schematically showing still another example ofa part of the process of producing an ultra-low refractive index layerof the present invention and still another example of the apparatus usedtherefor.

FIG. 6 is an illustration schematically showing still another example ofa part of the process of producing an ultra-low refractive index layerof the present invention and still another example of the apparatus usedtherefor.

FIG. 7 is a process cross sectional view schematically showing stillanother example of the method of forming an ultra-low refractive indexlayer on a base in the present invention.

FIG. 8 is an illustration schematically showing still another example ofa part of the process of producing an ultra-low refractive index layerof the present invention and still another example of the apparatus usedtherefor.

FIG. 9 is an illustration schematically showing still another example ofa part of the process of producing an ultra-low refractive index layerof the present invention and still another example of the apparatus usedtherefor.

DETAILED DESCRIPTION OF THE INVENTION

In the ultra-low refractive index layer of the laminated film roll ofthe present invention, for example, the abrasion resistance showing afilm strength, measured with BEMCOT® is in the range from 60% to 100%and the folding endurance showing flexibility, measured by the MIT testis 100 times or more.

In the ultra-low refractive index layer of the laminated film roll ofthe present invention, one kind or two or more kinds of structural unitsthat form a structure with minute void spaces may be chemically bonded.The chemical bond among the structural units may include a direct bondor an indirect bond, for example. Note that, in the ultra-low refractiveindex layer of the laminated film roll of the present invention, it isonly required that at least some of the structural units are chemicallybonded, for example. Specifically, there may be a part at which thestructural units are in contact with each another but not chemicallybonded, for example. Note that, in the present invention, “thestructural units are “indirectly bonded”” means that the structuralunits are bonded through binder components each of which is smaller inamount than the amount of the structural unit. On the other hand, “thestructural units are “directly bonded”” means that the structural unitsare bonded one another directly without involving binder components andthe like.

In the ultra-low refractive index layer of the laminated film roll ofthe present invention, for example, the bond among the structural unitsincludes a hydrogen bond or a covalent bond. The structural units may bein the shape of at least one of a particle, fiber, and a plate, forexample. Each of the structural unit in the shape of a particle and thestructural unit in the shape of a plate may be made of an inorganicmatter, for example. The configuration element of the structural unit inthe shape of a particle may include at least one element selected fromthe group consisting of Si, Mg, Al, Ti, Zn, and Zr, for example. Thestructure (structural unit) in the shape of a particle may be a solidparticle or a hollow particle, and specific examples thereof includesilicon particles, silicon particles with micropores, silica hollownanoparticles, and silica hollow nanoballoons. The structural unit inthe shape of fiber can be, for example, nanofiber having a nano-sizeddiameter, and specific examples thereof include cellulose nanofiber andalumina nanofiber. The structural unit in the shape of a plate can be,for example, nanoclay. Specifically, the structural unit in the shape ofa plate can be, for example, nano-sized bentonite (for example, KunipiaF [product name]). The structural unit in the shape of fiber may be atleast one selected from the group consisting of carbon nanofiber,cellulose nanofiber, alumina nanofiber, chitin nanofiber, chitosannanofiber, polymer nanofiber, glass nanofiber, and silica nanofiber, forexample, although it is not particularly limited.

The ultra-low refractive index layer of the laminated film roll of thepresent invention is, for example, a porous body containing microporousparticles. In the present invention, the shape of the “particle” (forexample, the microporous particle) is not limited to particular shapes,and can be, for example, a spherical shape, a non-spherical shape, andthe like. Furthermore, in the present invention, the microporousparticle may be, for example, a sol-gel beaded particle, a nanoparticle(hollow nanosilica/nanoballoon particle), nanofiber, and the like asdescribed above.

The ultra-low refractive index layer of the laminated film roll of thepresent invention has a proportion of void space of 40% or more, forexample.

The laminated film roll of the present invention has a pore size in therange from 2 to 200 nm, for example.

The laminated film roll of the present invention has a thickness in therange from 0.01 to 100 μm, for example.

The laminated film roll of the present invention has a haze showingtransparency of less than 5%, for example.

The method of producing a laminated film roll of the present inventionfurther comprises a step of adding a catalyst for chemically bonding themicroporous particles to the liquid in the liquid preparing step, forexample.

In the method of producing a laminated film roll of the presentinvention, for example, the catalyst is a catalyst for promoting thecrosslinking bond among the microporous particles.

In the method of producing a laminated film roll of the presentinvention, for example, the structural units are directly bonded to formthe ultra-low refractive index layer.

In the method of producing a laminated film roll of the presentinvention, for example, the structural units are indirectly bonded toform the ultra-low refractive index layer.

In the method of producing a laminated film roll of the presentinvention, for example, the ultra-low refractive index layer is formedsuch that the bond among the structural units includes a hydrogen bondor a covalent bond.

In the method of producing a laminated film roll of the presentinvention, for example, the structural units are in the shape of atleast one of a particle, fiber, and a plate. Each of the structural unitin the shape of a particle and the structural unit in the shape of aplate may be made of an inorganic matter, for example. The configurationelement of the structural unit in the shape of a particle may include atleast one element selected from the group consisting of Si, Mg, Al, Ti,Zn, and Zr, for example. The structural unit may include a microporousparticle, for example.

The present invention is described below in more detail with referenceto illustrative examples. The present invention, however, is not limitedor restricted by the following description.

[1. Laminated Film Roll]

The laminated film roll of the present invention includes: an ultra-lowrefractive index layer having a refractive index of 1.20 or less; and aresin film, wherein the ultra-low refractive index layer is stacked onthe resin film as described above. Instead of this, as described above,the present invention may be a laminated film including: an ultra-lowrefractive index layer having a refractive index of 1.20 or less; and aresin film, wherein the ultra-low refractive index layer is stacked onthe resin film, the abrasion resistance showing a film strength,measured with BEMCOT® is in the range from 60% to 100% and the foldingendurance showing flexibility, measured by the MIT test is 100 times ormore.

The resin film is not limited to particular resin films, and examples ofthe resin include thermoplastic resins with superior transparency suchas polyethylene terephthalate (PET), acryl, cellulose acetate propionate(CAP), cycloolefin polymer (COP), triacetate (TAC), polyethylenenaphthalate (PEN), polyethylene (PE), and polypropylene (PP).

The ultra-low refractive index layer (hereinafter, also referred to asan “ultra-low refractive index layer of the present invention”) of thelaminated film roll or the laminated film of the present invention maybe directly stacked on the resin film or indirectly stacked on the resinfilm through another layer, for example.

When the ultra-low refractive index layer of the present invention isformed on the resin film, for example, the present invention can be alow refractive material having the above-described properties,including: the ultra-low refractive index layer and the resin film,wherein the ultra-low refractive index layer is stacked on the resinfilm, for example.

The ultra-low refractive index layer of the present invention has anabrasion resistance showing a film strength, measured with BEMCOT® inthe range from 60% to 100% as described above. The present inventionhaving such a film strength is resistant to a physical impact in windingduring production and in use, for example. The lower limit of theabrasion resistance is, for example, 60% or more, 80% or more, or 90% ormore, the upper limit thereof is, for example, 100% or less, 99% orless, or 98% or less, and the abrasion resistance is, for example, inthe range from 60% to 100%, 80% to 99%, or 90% to 98%.

In the ultra-low refractive index layer of the laminated film roll orthe laminated film of the present invention, for example, the abrasionresistance showing a film strength, measured with BEMCOT® is in therange from 60% to 100% and the folding endurance showing flexibility,measured by an MIT test is 100 times or more. When the ultra-lowrefractive index layer includes silicon (Si), for example, the abrasionresistance can be measured according to the method described below. Whenthe ultra-low refractive index layer includes an element other thansilicon (Si), for example, the abrasion resistance can be measured withreference to the method described below.

(Evaluation of Abrasion Resistance)

(1) A void-provided layer (the ultra-low refractive index layer of thepresent invention) formed on an acrylic film by coating is cut into acircle having a diameter of about 15 mm as a sample.

(2) Next, as to the sample, the coating amount of Si (Si₀) is measuredby identifying silicon by X-ray fluorescence (product of ShimadzuCorporation, product name: ZSX Primus II). Subsequently, thevoid-provided layer on the acrylic film in proximity to the site wherethe circular sample was obtained is cut so as to have a piece having asize of 50 mm×100 mm, the obtained piece is fixed to a glass plate(thickness: 3 mm), and a sliding test is performed using BEMCOT®. Thesliding condition is as follows: weight: 100 g, reciprocation: 10 times.(3) The sampling and X-ray fluorescence measurement of the void-providedlayer after finishing sliding are performed in the same manner as theabove described item (1) to measure the residual amount of Si (Si₁)after an abrasion test. The abrasion resistance is defined by theresidual ratio of Si (%) before and after the sliding test usingBEMCOT®, and is represented by the following formula.abrasion resistance (%)=[residual amount of Si (Si₁)/Si coating amount(Si₀)]×100(%)

The folding endurance of the ultra-low refractive index layer of thepresent invention measured by the MIT test is, for example, 100 times ormore as described above. The folding endurance shows flexibility, forexample. Since the present invention has such flexibility, for example,a superior winding ability in continuous production and a superiorhandleability in use can be achieved, for example.

The lower limit of the folding endurance is, for example, 100 times ormore, 500 times or more, or 1000 times or more, the upper limit of thefolding endurance is not limited to particular values and is, forexample, 10000 times or less, and the folding endurance is, for example,in the range from 100 to 10000 times, 500 to 10000 times, or 1000 to10000 times.

The flexibility means deformability of a substance, for example. Thefolding endurance by the MIT test can be measured, for example, by themethod described below.

(Evaluation of Folding Endurance Test)

The void-provided layer (the ultra-low refractive index layer of thepresent invention) is cut into a piece having a size of 20 mm×80 mm,then the obtained piece is attached to a MIT folding endurance tester(production of TESTER SANGYO CO., LTD., product name: BE-202), and 1.0 Nload is applied thereto. A chuck of R 2.0 mm for holding thevoid-provided layer is used, application of load is at most 10000 times,and the number of times of application of load at the time of fractureof the void-provided layer is assumed as the folding endurance.

The film density of the ultra-low refractive index layer of the presentinvention is not limited to particular values, and the lower limitthereof is, for example, 1 g/cm³ or more, 10 g/cm³ or more, 15 g/cm³ ormore, the upper limit thereof is, for example, 50 g/cm³ or less, 40g/cm³ or less, or 30 g/cm³ or less, or 2.1 g/cm³ or less, and the filmdensity is, for example, in the range from 5 to 50 g/cm³, 10 to 40g/cm³, 15 to 30 g/cm³, or 1 to 2.1 g/cm³. In the ultra-low refractiveindex layer of the present invention, the lower limit of the porositybased on the film density is, for example, 50% or more, 70% or more, or85% or more, the upper limit thereof is, for example, 98% or less or 95%or less, and the porosity is, for example, in the range from 50% to 98%,70% to 95%, or 85% to 95%.

The film density can be measured, for example, by the method describedbelow, and the porosity can be calculated, for example, as describedbelow based on the film density.

(Evaluation of Film Density and Porosity)

After forming a void-provided layer (the ultra-low refractive indexlayer of the present invention) on a base (acrylic film), the X-rayreflectivity in a total reflection region of the void-provided layer ofthis laminate is measured using an X-ray diffractometer (product ofRIGAKU, product name: RINT-2000). Then, after fitting with Intensity at20, the film density (g/cm³) is calculated from the total reflectionangle of the laminate (void-provided layer and base), and the porosity(P %) is calculated by the following formula.porosity (P %)=45.48×film density (g/cm³)+100(%)

The ultra-low refractive index layer has a pore structure. The size of avoid space (pore) in the present invention indicates not the diameter ofthe short axis but the diameter of the long axis of the void space. Thesize of a void space (pore) is preferably in the range from 2 nm to 500nm, for example. The lower limit of the size of a void space is, forexample, 2 nm or more, 5 nm or more, 10 nm or more, or 20 nm or more,the upper limit of the size of a void space is, for example, 500 nm orless, 200 nm or less, or 100 nm or less, and the size of a void spaceis, for example, in the range from 2 nm to 500 nm, 5 nm to 500 nm, 10 nmto 200 nm, or 20 nm to 100 nm. A preferable size of a void space changesdepending on applications of the void-provided structure. Thus, the sizeof a void space should be adjusted to a desired size according topurposes, for example. The size of a void space can be evaluated by themethod described below.

(Evaluation of Size of Void Space)

In the present invention, the size of a void space can be quantifiedaccording to the BET test. Specifically, 0.1 g of a sample (theultra-low refractive index layer of the present invention) is set in thecapillary of a surface area measurement apparatus (product ofMicromeritics, product name: ASAP 2020), and dried under a reducedpressure at room temperature for 24 hours to remove gas in thevoid-provided structure. Then, an adsorption isotherm is created byadsorbing a nitrogen gas to the sample, thereby obtaining a poredistribution. The size of a void space can thereby be evaluated.

It is only required that the ultra-low refractive index layer of thepresent invention has a pore structure (porous structure) as describedabove, for example, and the ultra-low refractive index layer may have anopen-cell structure in which the pore structures are interconnected, forexample. The open-cell structure means, for example, that the porestructures are three-dimensionally interconnected in the ultra-lowrefractive index layer (for example, silicon porous body) of the presentinvention, i.e., void spaces in the pore structures are interconnected.When a porous body has an open-cell structure, the porosity of the bulkbody can be increased. However, an open-cell structure cannot be formedwith closed-cell particles such as hollow silica. In this regard, forexample, when the silica sol particle (pulverized product of a gelledsilicon compound which forms sol) is used, since the particles have athree-dimensional dendritic structure, the ultra-low refractive indexlayer of the present invention can form an open-cell structure easily bysettlement and deposition of the dendritic particles in a coating film(sol coating film containing the pulverized products of a gelled siliconcompound). The ultra-low refractive index layer of the present inventionpreferably forms a monolith structure in which the open-cell structurehas multiple pore distributions. The monolith structure denotes ahierarchical structure including a structure in which nano-sized voidspaces are present and an open-cell structure in which the nano-sizedspaces are aggregated, for example. The monolith structure can impart afilm strength with minute void spaces while imparting a high porositywith coarse open-cell structure, which achieve both a film strength anda high porosity, for example. For forming such a monolith structure, forexample, it is preferable to control the pore distribution of avoid-provided structure to be created in a gel (gelled silicon compound)before pulverizing into the silica sol particles. For example, bycontrolling the particle size distribution of silica sol particles afterpulverization to a desired size in pulverization of the gelled siliconcompound, the monolith structure can be formed.

In the ultra-low refractive index layer of the present invention, thehaze showing transparency is not limited to particular values, and theupper limit thereof is, for example, less than 5% and preferably lessthan 3%, the lower limit thereof is, for example, 0.1% or more or 0.2%or more, and the haze is, for example, 0.1% or more and less than 5% or0.2% or more and less than 3%.

The haze can be measured, for example, by the method described below.

(Evaluation of Haze)

A void-provided layer (the ultra-low refractive index layer of thepresent invention) is cut into a piece having a size of 50 mm×50 mm, andthe obtained piece is set to a haze meter (product of Murakami ColorResearch Laboratory, product name: HM-150) to measure a haze. The hazevalue is calculated by the following formula.haze (%)=[diffuse transmittance (%)/total light transmittance(%)]×100(%)

Commonly, a ratio between the transmission speed of the wavefront oflight in vacuum and the phase velocity of light in a medium is called arefractive index of the medium. The upper limit of the refractive indexof the ultra-low refractive index layer of the present invention is, forexample, 1.20 or less or 1.15 or less, the lower limit thereof is, forexample, 1.05 or more, 1.06 or more, or 1.07 or more, and the refractiveindex is, for example, in the range from 1.05 to 1.20, 1.06 to 1.20, or1.07 to 1.15.

In the present invention, the refractive index is a refractive indexmeasured at the wavelength of 550 nm unless otherwise stated. The methodof measuring a refractive index is not limited to particular methods,and the refractive index can be measured, for example, by the methoddescribed below.

(Evaluation of Refractive Index)

After forming a void-provided layer (the ultra-low refractive indexlayer of the present invention) on an acrylic film, the obtainedlaminate is cut into a piece having a size of 50 mm×50 mm, and theobtained piece is adhered on the front surface of a glass plate(thickness: 3 mm) through a pressure-sensitive adhesive layer. Thecenter of the back surface of the glass plate (diameter: about 20 mm) issolidly painted with a black magic marker, thereby preparing a samplewhich allows no reflection at the back surface of the glass plate. Thesample is set to an ellipsometer (product of J.A. Woollam Japan, productname: VASE), the refractive index is measured at the wavelength of 500nm and at the incidence angle of 50° to 80°, and the average value isassumed as a refractive index.

When the ultra-low refractive index layer of the present invention isformed on the resin film, for example, the peel strength showingadhesion between the ultra-low refractive index layer and the resin filmis not limited to particular values, and the lower limit thereof is, forexample, 1 N/25 mm or more, 2 N/25 mm or more, or 3 N/25 mm or more, theupper limit thereof is, for example, 30 N/25 mm or less, 20 N/25 mm orless, or 10 N/25 mm or less, and the peel strength is, for example, inthe range from 1 to 30 N/25 mm, 2 to 20 N/25 mm, or 3 to 10 N/25 mm.

The method of measuring the peel strength is not limited to particularmethods, and the peel strength can be measured by the method describedbelow, for example.

(Evaluation of Peel Strength)

After forming the void-provided layer (the ultra-low refractive indexlayer of the present invention) on the resin film (for example, acrylicfilm), a piece having a size of 50 mm×140 mm is obtained as a sample andthe sample is fixed to a stainless plate with a double-sided tape. Anacrylic pressure-sensitive adhesive layer (thickness 20 μm) is adheredto a PET film (product of Mitsubishi Plastics, Inc., product name:T100), the thus obtained adhesive tape is cut into a piece having a sizeof 25 mm×100 mm, and the obtained piece is adhered to the void-providedlayer to form a laminate of the PET film and the void-provided layer.Then, the sample is chucked in a tensile testing machine (product ofShimadzu Corporation, product name: AG-Xplus) with a chuck space of 100mm, and the tensile test is performed at the tensile speed of 0.3 m/min.The average of 50 mm peel test is assumed as the peel strength.

The thickness of the ultra-low refractive index layer of the presentinvention is not limited to particular values, and the lower limitthereof is, for example, 0.01 μm or more, 0.05 μm or more, 0.1 μm ormore, or 0.3 μm or more, the upper limit thereof is, for example, 100 μmor less, 80 μm or less, 50 μm or less, or 10 μm or less, and thethickness is, for example, in the range from 0.01 to 100 μm.

As described above, the ultra-low refractive index layer of the presentinvention includes pulverized products of a gelled compound, wherein thepulverized products are chemically bonded by catalysis, for example. Inthe ultra-low refractive index layer of the present invention, thepattern of the chemical bond among the pulverized products is notlimited to particular patterns. Specifically, the chemical bond can be,for example, a crosslinking bond. The method of chemically bonding thepulverized products is described in detail in the description as to theproduction method of the present invention.

The gel form of the gelled compound is not limited to particular forms.The “gel” commonly denotes a solidified state of solutes aggregated asthey lost independent motility due to interaction. Commonly, a wet gelis a gel containing a dispersion medium in which solutes build a uniformstructure, and a xerogel is a gel from which a solvent is removed and inwhich solutes form a network structure with void spaces. In the presentinvention, the gelled compound can be a wet gel or a xerogel, forexample.

The gelled compound can be, for example, a gelled product obtained bygelating monomer compounds. Specifically, the gelled silicon compoundcan be, for example, a gelled product in which the monomer siliconcompounds are bonded. As a specific example, the gelled silicon compoundcan be a gelled product in which the monomer silicon compounds arebonded by a hydrogen bond or an intermolecular bond. The bond can be,for example, a bond by dehydration condensation. The method of gelationis described below in the description as to the production method of thepresent invention.

In the ultra-low refractive index layer of the present invention, thevolume average particle size showing particle size variations of thepulverized product is not limited to particular values, and the lowerlimit thereof is, for example, 0.10 μm or more, 0.20 μm or more, or 0.40μm or more, the upper limit thereof is, for example, 2.00 μm or less,1.50 μm or less, or 1.00 μm or less, and the volume average particlesize is, for example, in the range from 0.10 μm to 2.00 μm, 0.20 μm to1.50 μm, or 0.40 μm to 1.00 μm. The particle size distribution can bemeasured, for example, using a particle size distribution analyzer basedon dynamic light scattering, laser diffraction, or the like or using anelectron microscope such as a scanning electron microscope (SEM) or atransmission electron microscope (TEM).

The particle size distribution showing particle size variations of thepulverized product is not limited to particular values. The distributionof the particle having a particle size of 0.4 μm to 1 μm is in the rangefrom 50 wt % to 99.9 wt %, 80 wt % to 99.8 wt %, or 90 wt % to 99.7 wt %or the distribution of the particle having a particle size of 1 μm to 2μm is in the range from 0.1 wt % to 50 wt %, 0.2 wt % to 20 wt %, or 0.3wt % to 10 wt %, for example. The particle size distribution can bemeasured, for example, using a particle size distribution analyzer or anelectron microscope.

In the ultra-low refractive index layer of the present invention, thetype of the gelled compound is not limited to particular types. Thegelled compound can be, for example, a gelled silicon compound. Thepresent invention is described below with reference to an example inwhich the gelled compound is a gelled silicon compound. The presentinvention, however, is not limited thereto.

The crosslinking bond is, for example, a siloxane bond. Examples of thesiloxane bond include T2 bond, T3 bond, and T4 bond shown below. In thecase where the ultra-low refractive index layer of the present inventionhas the siloxane bond, the porous body of the present invention may haveone of, two of, or all of the above-mentioned three bond patterns, forexample. The silicone porous body having higher proportions of T2 and T3is superior in flexibility and can be expected to have an originalproperty of a gel but is inferior in film strength. On the other hand,the silicone porous body having a higher proportion of T4 is superior infilm strength but has small sized void spaces and is inferior inflexibility. Thus, it is preferable to change the proportions of T2, T3,and T4 depending on applications, for example.

In the case where the ultra-low refractive index layer of the presentinvention has the siloxane bond, the relative ratio among T2, T3, and T4with T2 being considered as “1” is, for example, as follows:T2:T3:T4=1:[1 to 100]:[0 to 50], 1:[1 to 80]:[1 to 40], or 1:[5 to60]:[1 to 30].

The silicon atoms contained in the ultra-low refractive index layer ofthe present invention are preferably bonded by a siloxane bond, forexample. As a specific example, the proportion of the unbonded siliconatoms (i.e., residual silanol) among all the silicon atoms contained inthe ultra-low refractive index layer is, for example, less than 50%, 30%or less, or 15% or less.

When the gelled compound is the gelled silicon compound, the monomersilicon compound is not limited to particular compounds. The monomersilicon compound can be, for example, a compound represented by thefollowing chemical formula (1). When the gelled silicon compound is agelled product in which monomer silicon compounds are bonded by ahydrogen bond or an intermolecular bond as described above, monomers inthe chemical formula (1) can be bonded by a hydrogen bond through theirhydroxyl groups, for example.

In the chemical formula (1), for example, X is 2, 3, or 4, and R¹represents a linear or a branched alkyl group. The carbon number of R¹is, for example, 1 to 6, 1 to 4, or 1 to 2. Examples of the linear alkylgroup include a methyl group, an ethyl group, a propyl group, a butylgroup, a pentyl group, and a hexyl group, and examples of the branchedalkyl group include an isopropyl group and an isobutyl group. The X is,for example, 3 or 4.

A specific example of the silicon compound represented by the chemicalformula (1) can be a compound represented by the chemical formula (1′),wherein X is 3. In the chemical formula (1′), R¹ is the same as that inthe chemical formula (1), and is, for example, a methyl group. When R¹represents a methyl group, the silicon compound istris(hydroxy)methylsilane. When X is 3, the silicon compound is, forexample, trifunctional silane having three functional groups.

A specific example of the silicon compound represented by the chemicalformula (1) can be a compound represented by the chemical formula (1′)wherein X is 4. In this case, the silicon compound is, for example,tetrafunctional silane having four functional groups.

The monomer silicon compound may be, for example, a hydrolysate of asilicon compound precursor. The silicon compound precursor is notlimited as long as it can generate the silicon compound by hydrolysis,for example. A specific example of the silicon compound precursor can bea compound represented by the following chemical formula (2).

In the chemical formula (2), for example, X is 2, 3, or 4, R¹ and R²each represent a linear or branched alkyl group, R¹ and R² may be thesame or different, R¹ may be the same or different in the case where Xis 2, and R² may be the same or different.

X and R¹ are the same as those in the chemical formula (1), for example.Regarding R², for example, reference can be made to the examples of R¹in the chemical formula (1).

A specific example of the silicon compound precursor represented by thechemical formula (2) can be a compound represented by the chemicalformula (2′) wherein X is 3. In the chemical formula (2′), R¹ and R² arethe same as those in the chemical formula (2). When R¹ and R² bothrepresent methyl groups, the silicon compound precursor istrimethoxy(methyl)silane (hereinafter, also referred to as “MTMS”).

The monomer silicon compound is preferably the trifunctional silanebecause it is superior in the lowness of refractive index. Also, themonomer silicon compound is preferably the tetrafunctional silanebecause it is superior in strength (for example, abrasion resistance).Regarding the monomer silicon compounds which are raw materials of thegelled silicon compound, one of the compounds may be used alone or twoor more of them may be used in combination, for example. As a specificexample, the monomer silicon compound may include only the trifunctionalsilane, only the tetrafunctional silane, or both of the trifunctionalsilane and the tetrafunctional silane, and may further include othersilicon compounds, for example. When two or more kinds of siliconcompounds are used as the monomer silicon compound, the ratio betweenthe compounds is not limited to particular values and can be determinedappropriately.

The ultra-low refractive index layer of the present invention maycontain a catalyst for chemically bonding one kind or two or more kindsof structural units that form a structure with minute void spaces, forexample. The content of the catalyst is not limited to particularvalues, and the content of the catalyst relative to the weight of thestructural unit is, for example, 0.01 wt % to 20 wt %, 0.05 wt % to 10wt %, or 0.1 wt % to 5 wt %.

The ultra-low refractive index layer of the present invention mayfurther contain a crosslinking assisting agent for indirectly bondingone kind or two or more kinds of structural units that form a structurewith minute void spaces, for example. The content of the crosslinkingassisting agent is not limited to particular values, and the content ofthe crosslinking assisting agent relative to the weight of thestructural unit is, for example, 0.01 wt % to 20 wt %, 0.05 wt % to 15wt %, or 0.1 wt % to 10 wt %.

The form of the ultra-low refractive index layer of the presentinvention is not limited to particular forms, and is normally in theform of a film.

The ultra-low refractive index layer of the present invention is, forexample, a roll. For example, the present invention may further includea resin film, and the ultra-low refractive index layer may be formed onthe long resin film as described above. In this case, another long filmmay be stacked on the laminated film of the present invention.Specifically, another long resin film (for example, interleaving paper,release film, surface protection film, or the like) may be stacked onthe laminated film of the present invention including the resin film andthe ultra-low refractive index layer, and then the obtained laminate maybe wound in the form of a roll.

The method of producing a laminated film roll of the present inventionis not limited to particular methods, and the laminated film of thepresent invention can be produced, for example, by the production methodof the present invention described below.

[2. Production Method of Laminated Film Roll]

The method of forming a laminated film roll of the present inventionpreferably includes steps of: preparing a liquid containing microporousparticles; coating a resin film with the liquid; and drying the liquidapplied on the resin film as described above. The present invention,however, is not limited thereto. The liquid containing the microporousparticles (hereinafter may be also referred to as a “microporousparticle-containing liquid”) is not limited to particular liquids, andcan be, for example, a suspension containing the microporous particles.The present invention is described below mainly with reference to anexample in which the microporous particle is a pulverized product of agelled compound and the ultra-low refractive index layer is a porousbody (preferably, silicone porous body) including pulverized products ofa gelled compound. The present invention, however, can be performed inthe same manner also in the case where the microporous particle issomething other than the pulverized product of a gelled compound. In theproduction method of the laminated film roll of the present invention,the ultra-low refractive index layer is, for example, a porous body inwhich microporous particles are chemically bonded, and the microporousparticles are chemically bonded in the ultra-low refractive index layerforming step. The microporous particle is, for example, a siliconcompound microporous particle and the porous body is a silicone porousbody. The silicon compound microporous particle includes, for example, apulverized product of a gelled silica compound. Another embodiment ofthe ultra-low refractive index layer includes a void-provided layerincluding fibrous substances such as nanofiber, wherein the fibroussubstances are entangled to form a layer with void spaces. Theproduction method of a void-provided layer including fibrous substancesis the same as that of the layer including microporous particles.Besides the aforementioned embodiment, the ultra-low refractive indexlayer includes a void-provided layer formed by using hollownanoparticles and nanoclay, and a void-provided layer made by usinghollow nanoballoons and magnesium fluoride. These ultra-low refractiveindex layers may be void-provided layers made of a single configurationsubstance or of multiple configuration substances. The void-providedlayer may be the layer adopting one of the aforementioned embodiments orthe layer adopting more than one of the aforementioned embodiments. Thepresent invention is described below mainly with reference to thevoid-provided layer of a porous body in which the microporous particlesare chemically bonded.

The production method of the present invention forms an ultra-lowrefractive index layer which is superior in the lowness of refractiveindex. The following theory about the reason for this can be formed. Thepresent invention, however, is not limited thereto.

Since the pulverized product used in the production method of thepresent invention is obtained by pulverizing the gelled siliconcompound, the three-dimensional structure of the gelled silicon compoundbefore pulverization is dispersed into three-dimensional basicstructures. In the production method of the present invention, theprecursor having a porous structure based on the three-dimensional basicstructures is formed by coating the base with the pulverized products ofa gelled silicon compound. That is, according to the production methodof the present invention, a new porous structure is formed of thepulverized products each having the three-dimensional basic structure,which is different from the three-dimensional structure of the gelledsilicon compound. Thus, the finally obtained ultra-low refractive indexlayer brings about an effect of a low refractive index equivalent to anair layer, for example. Moreover, in the production method of thepresent invention, since the pulverized products are chemically bonded,the new three-dimensional structure is immobilized. Thus, the finallyobtained ultra-low refractive index layer, despite its structure withvoid spaces, can maintain a sufficient strength and sufficientflexibility. The ultra-low refractive index layer obtained by theproduction method of the present invention is useful as a substitute forthe air layer, in an aspect of low refractive index as well as instrength and flexibility, for example. In the case of an air layer, theair layer is formed between the components by stacking components with aspace by providing a spacer or the like therebetween. The ultra-lowrefractive index layer obtained by the production method of the presentinvention can achieve a low refractive index equivalent to the air layeronly by disposing it at a desired site, for example. Thus, as describedabove, the present invention can impart a low refractive indexequivalent to the air layer easier and simpler than forming the airlayer.

Regarding the production method of the present invention, reference canbe made to the description as to the ultra-low refractive index layer ofthe present invention unless otherwise stated.

Regarding the gelled compound, the pulverized product thereof, themonomer compound, and the precursor of the monomer compound in theproduction method of the present invention, reference can be made to thedescription as to the porous structure of the present invention.

The production method of the present invention includes a step ofpreparing a liquid containing microporous particles as described above.When the microporous particle is a pulverized product of a gelledcompound, the pulverized product can be obtained, for example, bypulverizing the gelled compound. By pulverization of the gelledcompound, as described above, the three-dimensional structure of thegelled compound is destroyed and dispersed into three-dimensional basicstructures.

Generation of the gelled compound by gelation of the monomer compoundand preparation of the pulverized product by pulverization of the gelledcompound are described below. The present invention, however, is notlimited thereto.

The gelation of the monomer compound can be performed, for example, bybonding the monomer compounds by a hydrogen bond or an intermolecularbond.

The monomer compound can be, for example, a silicon compound representedby the chemical formula (1) described in the description as to theultra-low refractive index layer of the present invention.

Since the silicon compound represented by the chemical formula (1) has ahydroxyl group, monomers in the chemical formula (1) can be bonded by ahydrogen bond or an intermolecular bond through their hydroxyl groups,for example.

The silicon compound may be the hydrolysate of the silicon compoundprecursor as described above, and may be generated by hydrolyzing thesilicon compound precursor represented by the chemical formula (2)described in the description as to the ultra-low refractive index layerof the present invention, for example.

The method of hydrolyzing the monomer compound precursor is not limitedto particular methods, and can be performed by a chemical reaction inthe presence of a catalyst, for example. Examples of the catalystinclude acids such as an oxalic acid and an acetic acid. The hydrolysisreaction can be performed, for example, by gradually dropping an oxalicacid aqueous solution to a mixture (for example, suspension) of thesilicon compound and dimethylsulfoxide to mix at room temperature, andstirring the resultant for about 30 minutes. In hydrolysis of thesilicon compound precursor, for example, by completely hydrolyzing thealkoxy group of the silicon compound precursor, gelation and agingthereafter and heating and immobilization after formation of avoid-provided structure can be achieved more efficiently.

The gelation of the monomer compound can be performed, for example, by adehydration condensation reaction among the monomers. The dehydrationcondensation reaction is preferably performed in the presence of acatalyst, for example. Examples of the catalyst include dehydrationcondensation catalysts such as: acid catalysts including a hydrochloricacid, an oxalic acid, and a sulfuric acid; and base catalysts includingammonia, potassium hydroxide, sodium hydroxide, and ammonium hydroxide.The dehydration condensation catalyst is particularly preferably a basecatalyst. In the dehydration condensation reaction, the amount of thecatalyst to be added to the monomer compound is not limited toparticular values, and is, for example, 0.1 to 10 mol, 0.05 to 7 mol, or0.1 to 5 mol per mol of the monomer compound.

The gelation of the monomer compound is preferably performed in asolvent, for example. The proportion of the monomer compound in thesolvent is not limited to particular values. Examples of the solventinclude dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP),N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), γ-butyrolactone(GBL), acetonitrile (MeCN), and ethylene glycol ethyl ether (EGEE). Oneof the solvents may be used alone or two or more of them may be used incombination, for example. Hereinafter, the solvent used for the gelationis also referred to as a “gelation solvent”.

The condition for the gelation is not limited to particular conditions.Regarding the treatment of the solvent containing the monomer compound,the treatment temperature is, for example, 20° C. to 30° C., 22° C. to28° C., or 24° C. to 26° C., and the treatment time is, for example, 1to 60 minutes, 5 to 40 minutes, or 10 to 30 minutes. The treatmentcondition for the dehydration condensation reaction is not limited toparticular conditions, and reference can be made to these examples. Bygelation, a siloxane bond is grown and silica primary particles areformed. As the reaction further proceeds, the primary particles areconnected in the form of a string of beads to generate a gel having athree-dimensional structure, for example.

The gelled compound obtained by the gelation is preferably subjected toaging treatment after the gelation reaction. The aging treatment causesfurther growth of the primary particle of a gel having athree-dimensional structure obtained by gelation, for example, and thisallows the size of the particle itself to be increased. As a result, thecontact state of the neck where particles are in contact with oneanother can be increased from a point contact to a surface contact. Thegel which has been subjected to the aging treatment increases itsstrength, for example, and this increases the strength of thethree-dimensional basic structure after pulverization. This prevents, inthe drying step after coating of the pulverized product, the pore sizeof the void-provided structure obtained by deposition of thethree-dimensional basic structures from shrinking in accordance withsolvent volatilization during the drying process, for example.

The aging treatment can be performed, for example, by incubating thegelled compound at a predetermined temperature for a predetermined time.The predetermined temperature is not particularly limited, and the lowerlimit thereof is, for example, 30° C. or more, 35° C. or more, or 40° C.or more, the upper limit thereof is, for example, 80° C. or less, 75° C.or less, or 70° C. or less, and the predetermined temperature is, forexample, in the range from 30° C. to 80° C., 35° C. to 75° C., or 40° C.to 70° C. The predetermined time is not particularly limited, and thelower limit is, for example, 5 hours or more, 10 hours or more, or 15hours or more, the upper limit is, for example, 50 hours or less, 40hours or less, or 30 hours or less, and the predetermined time is, forexample, in the range from 5 hours to 50 hours, 10 hours to 40 hours, or15 hours to 30 hours. An optimal condition for the aging is, forexample, the condition mainly aiming for increase in the size of thesilica primary particle and increase in the contact area of the neck.Furthermore, it is preferable to take the boiling point of a solvent tobe used into consideration. For example, when the aging temperature istoo high, there is a possibility that the solvent excessivelyvolatilizes, which causes defectiveness such that the pore of thethree-dimensional void-provided structure closes due to the condensationof the concentration of a coating liquid (gel liquid). On the otherhand, for example, when the aging temperature is too low, there is apossibility not only that a sufficient effect of the aging is notbrought about but also that temperature variations over time in a massproduction process increase, which causes products with poor quality tobe produced.

The same solvent as the solvent used in the gelation treatment can beused in the aging treatment, for example. Specifically, the agingtreatment is preferably applied to a reactant (the solvent containingthe gelled compound) after the gelation treatment. The mol number ofresidual silanol groups contained in the gel (the gelled compound, forexample, the gelled silicon compound) after completion of the agingtreatment after gelation is, for example, the proportion of the residualsilanol group with the mol number of alkoxy groups of the added rawmaterial (for example, the monomer compound precursor) being consideredas 100, and the lower limit thereof is, for example, 50% or more, 40% ormore, or 30% or more, the upper limit thereof is, for example, 1% orless, 3% or less, or 5% or less, and the mol number is, for example, inthe range from 1% to 50%, 3% to 40%, or 5% to 30%. For the purpose ofincreasing the hardness of a gel, for example, the lower the mol numberof the residual silanol groups, the better. When the mol number of thesilanol groups is too high, for example, there is a possibility that thevoid-provided structure cannot be held until crosslinking is done in theprecursors of the silicone porous body. On the other hand, when the molnumber of the silanol groups is too low, for example, there is apossibility that the pulverized products of the gelled compound cannotbe crosslinked in a step of preparing the liquid containing microporousparticles (for example, suspension) and/or subsequent steps, whichhinders a sufficient film strength from being imparted. Note that whilethe aforementioned description is described with reference to a silanolgroup as an example, the same phenomenon shall be applied to variousfunctional groups in the case where a monomer silicon compound ismodified with various reactive functional groups, for example.

After gelation of the monomer compound in the gelation solvent, theobtained gelled compound is pulverized. The gelled compound in thegelation solvent which has not been processed may be pulverized or thegelation solvent may be substituted with another solvent and the gelledcompound in the substituted solvent may be pulverized, for example.Furthermore, if the catalyst and solvent used in the gelation reactionremain after the aging step, which causes gelation of the liquid overtime (pot life) and decreases the drying efficiency in the drying step,it is preferable to substitute the gelation solvent with anothersolvent. Hereinafter, such a solvent for substitution may be alsoreferred to as a “pulverization solvent”.

The pulverization solvent is not limited to particular solvents, and canbe, for example, an organic solvent. The organic solvent can be, forexample, a solvent having a boiling point at 130° C. or less, 100° C. orless, or 85° C. or less. Specific examples of the organic solventinclude isopropyl alcohol (IPA), ethanol, methanol, butanol, propyleneglycol monomethyl ether (PGME), methyl cellosolve, acetone, anddimethylformamide (DMF). One of the pulverization solvents may be usedalone or two or more of them may be used in combination.

The combination of the gelation solvent and the pulverization solvent isnot limited to particular combinations, and the combination can be, forexample, the combination of DMSO and IPA, the combination of DMSO andethanol, the combination of DMSO and methanol, and the combination ofDMSO and butanol. Substitution of the gelation solvent with thepulverization solvent makes it possible to form a coating film withuniform quality in the coating film formation described below, forexample.

The method of pulverizing the gelled compound is not limited toparticular methods. Examples of the apparatus for pulverizing include:pulverizing apparatuses utilizing a cavitation phenomenon such as anultrasonic homogenizer and a high-speed rotating homogenizer; andpulverizing apparatuses of causing oblique collision of liquids at ahigh pressure. An apparatus such as a ball mill that performs mediapulverization physically destroys the void-provided structure of a gelin pulverization, for example. On the other hand, a cavitation-typepulverizing apparatus such as a homogenizer, which is preferable in thepresent invention, peels the contact surface of silica particles, whichare already contained in a gel three-dimensional structure and bondedrelatively weakly, with a high speed shearing force owing to a medialessmethod, for example. Thus, a sol three-dimensional structure to beobtained can hold the void-provided structure having a particle sizedistribution of a certain range and can form the void-provided structureagain by deposition in coating and drying, for example. The conditionfor the pulverization is not limited to particular conditions, and ispreferably a condition that allows a gel to be pulverized withoutvolatilizing a solvent by instantaneously imparting a high speed flow,for example. For example, it is preferable to pulverize the gelledsilicon compound so as to obtain pulverized products having the abovedescribed particle size variations (for example, volume average particlesize or particle size distribution). If the pulverization time, thepulverization strength, or the like is lacking, for example, there is apossibility not only that coarse particles remain, which hinders densepores from being formed but also that defects in appearance increase,which hinders high quality from being achieved. On the other hand, ifthe pulverization time, the pulverization strength, or the like is toomuch, for example, there is a possibility that a finer sol particle thana desired particle size distribution is obtained and the size of a voidspace deposited after coating and drying is too fine to satisfy adesired porosity.

In the manner described above, a liquid (for example, suspension)containing the microporous particles can be prepared. By further addinga catalyst for chemically bonding the microporous particles after orduring the preparation of the liquid containing the microporousparticles, a liquid containing the microporous particles and thecatalyst can be prepared. The amount of the catalyst to be added is notlimited to particular values, and the amount of the catalyst to be addedrelative to the weight of the microporous particle (pulverized productof the gelled silicon compound) is, for example, in the range from 0.01wt % to 20 wt %, 0.05 wt % to 10 wt %, or 0.1 wt % to 5 wt %. Thiscatalyst chemically bonds the microporous particles in the bonding stepdescribed below, for example. The catalyst may be, for example, acatalyst that promotes the crosslinking bond among the microporousparticles. As the chemical reaction of chemically bonding themicroporous particles, it is preferable to utilize the dehydrationcondensation reaction of a residual silanol group contained in a silicasol molecule. By promoting the reaction between the hydroxyl groups ofthe silanol group by the catalyst, the continuous formation of a film inwhich the void-provided structure is cured in a short time can beperformed. Examples of the catalyst include photoactive catalysts andthermoactive catalysts. The photoactive catalyst allows the chemicalbond (for example, crosslinking bond) among the microporous particleswithout heating, for example. This makes it possible to maintain ahigher proportion of void space because the shrinkage due to heating isless liable to occur, for example. In addition to or instead of thecatalyst, a substance (catalyst generator) that generates a catalyst maybe used. For example, the catalyst may be a crosslinking reactionaccelerator and the catalyst generator may be a substance that generatesthe crosslinking reaction accelerator. For example, in addition to orinstead of the photoactive catalyst, a substance (photocatalystgenerator) that generates a catalyst by light irradiation may be used.For example, in addition to or instead of the thermoactive catalyst, asubstance (thermal catalyst generator) that generates a catalyst byheating may be used. The photocatalyst generator is not limited toparticular photocatalyst generators, and examples thereof includephotobase generators (substances that generate basic catalysts by lightirradiation) and photoacid generators (substances that generate acidiccatalysts by light irradiation). Among them, the photobase generator ispreferable. Examples of the photobase generator include 9-anthrylmethylN,N-diethylcarbamate (product name: WPBG-018),(E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine (product name:WPBG-027), 1-(anthraquinon-2-yl)ethyl imidazolecarboxylate (productname: WPBG-140), 2-nitrophenylmethyl4-methacryloyloxypiperidine-1-carboxylate (product name: WPBG-165),1,2-diisopropyl-3-[bis(dimethylamino) methylene]guanidium2-(3-benzoylphenyl)propionate (product name: WPBG-266),1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium n-butyltriphenylborate(product name: WPBG-300), 2-(9-oxoxanthen-2-yl)propionic acid1,5,7-triazabicyclo[4.4.0] dec-5-ene (Tokyo Kasei Kogyo Co., Ltd.), anda compound containing 4-piperidinemethanol (product of Heraeus, productname: HDPD-PB100). Note here that each product with the name including“WPBG” is a product of Wako Pure Chemical Industries, Ltd. Examples ofthe photoacid generator include aromatic sulfonium salt (product ofADEKA, product name: SP-170), triarylsulfonium salt (product of San-AproLtd., product name: CPI101A), and aromatic iodonium salt (product ofCiba Japan, product name: Irgacure 250). The catalyst for chemicallybonding the microporous particles is not limited to the photoactivecatalyst, and can be, for example, a thermoactive catalyst such as urea.Examples of the catalyst for chemically bonding the microporousparticles include base catalysts such as potassium hydroxide, sodiumhydroxide, and ammonium hydroxide; and acid catalysts such as ahydrochloric acid, an acetic acid, and an oxalic acid. Among them, thebase catalyst is preferable. The catalyst for chemically bonding themicroporous particles can be used by adding it to a sol particle liquid(for example, suspension) containing the pulverized products(microporous particles) right before the coating, or the catalyst can beused as a mixture by mixing it with a solvent, for example. The mixturemay be, for example, a coating liquid obtained by adding the catalystdirectly to the sol particle liquid, a solution obtained by dissolvingthe catalyst in a solvent, or a dispersion liquid obtained by dispersingthe catalyst into a solvent. The solvent is not limited to particularsolvents, and examples thereof include various organic solvents, water,and buffer solutions.

For example, in the case where the microporous particle is a pulverizedproduct of a gelled silicon compound obtained from a silicon compoundcontaining at least three or less functional groups having saturatedbonds, a crosslinking assisting agent for indirectly bonding themicroporous particles may further be added after or during preparationof a liquid containing the microporous particles. This crosslinkingassisting agent penetrates among particles and interacts with or bondsto the particles, which helps to bond particles relatively distancedfrom one another and makes it possible to increase the strengthefficiently. As the crosslinking assisting agent, a multicrosslinkingsilane monomer is preferable. Specifically, the multicrosslinking silanemonomer may have at least two and at most three alkoxysilyl groups, thechain length between the alkoxysilyl groups may be 1-10C, and themulticrosslinking silane monomer may contain an element other thancarbon, for example. Examples of the crosslinking assisting agentinclude bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane,bis(trimethoxysilyl)methane, bis(triethoxysilyl)methane,bis(triethoxysilyl)propane, bis(trimethoxysilyl)propane,bis(triethoxysilyl)butane, bis(trimethoxysilyl)butane,bis(triethoxysilyl)pentane, bis(trimethoxysilyl)pentane,bis(triethoxysilyl)hexane, bis(trimethoxysilyl)hexane,bis(trimethoxysilyl)-N-butyl-N-propyl-ethane-1,2-diamine,tris-(3-trimethoxysilylpropyl)isocyanurate, andtris-(3-triethoxysilylpropyl)isocyanurate. The amount of thecrosslinking assisting agent to be added is not limited to particularvalues, and the amount of the crosslinking assisting agent to be addedrelative to the weight of the silicon compound microporous particle is,for example, in the range from 0.01 wt % to 20 wt %, 0.05 wt % to 15 wt%, or 0.1 wt % to 10 wt %.

The production method of the present invention includes a step ofcoating a resin film with the liquid containing the microporousparticles (for example, suspension) as described above. The coating canbe performed, for example, by the various coating methods describedbelow but not limited thereto. By directly coating the base with thesolvent containing the pulverized products, the precursor of the porousbody (coating film) can be formed. The precursor of the porous body canalso be referred to as a coating layer, for example. The precursor ofthe porous body, which is the precursor of the porous body before thebonding step described below, can be also referred to as a precursorfilm (or precursor layer) of the ultra-low refractive index layer of thepresent invention, for example. Formation of the precursor (coatingfilm) of the porous body causes the settlement and deposition of thepulverized product whose three-dimensional structure has been destroyed,for example, and this allows a new three-dimensional structure to beformed.

The solvent (hereinafter, also referred to as a “coating solvent”) isnot limited to particular solvents, and can be, for example, an organicsolvent. The organic solvent can be, for example, a solvent having aboiling point at 130° C. or less. Specific examples of the solventinclude IPA, ethanol, methanol, and butanol, and the examples of thepulverization solvent described above can be used. In the case where thepresent invention includes a step of pulverizing the gelled compound,for example, the pulverization solvent containing the pulverizedproducts of the gelled compound can be used without processing in thestep of forming the precursor of the porous body.

In the coating step, for example, it is preferable to coat the base withthe sol pulverized products dispersed in the solvent (hereinafter, alsoreferred to as a “sol particle liquid”). After coating the base with thesol particle liquid of the present invention and drying it, bychemically crosslinking the particles in the bonding step, thecontinuous formation of a void-provided layer having a film strength ofa certain level or more can be performed. The “sol” in the presentinvention denotes a fluidic state in which silica sol particles eachhaving a nano three-dimensional structure holding a part of thevoid-provided structure are dispersed in a solvent by pulverization ofthe three-dimensional structure of a gel.

The concentration of the pulverized product in the solvent is notlimited to particular values, and is, for example, in the range from0.3% to 50% (v/v), 0.5% to 30% (v/v), or 1.0% to 10% (v/v). When theconcentration of the pulverized product is too high, there is apossibility that the fluidity of the sol particle liquid decreasessignificantly, which causes aggregates and coating stripes in coating,for example. On the other hand, when the concentration of the pulverizedproduct is too low, there is a possibility not only that the drying ofthe sol particle solvent takes a relatively long time but also that theresidual solvent right after the drying increases, which may decreasethe porosity, for example.

There is no particular limitation on the physical property of the sol.The shear viscosity of the sol is, for example, 100 cPa·s or less, 10cPa·s or less, or 1 cPa·s or less, for example, at the shear rate of10001/s. When the shear viscosity is too high, for example, there is apossibility that the coating stripes are generated, which causesdefectiveness such as decrease in the transfer rate in the gravurecoating. In contrast, when the shear viscosity is too low, for example,there is a possibility that the thickness of the wet coating duringcoating cannot be increased and a desired thickness cannot be obtainedafter drying.

The coating amount of the pulverized product relative to the base is notlimited to particular values, and can be determined appropriately, forexample, according to the thickness of a desired silicone porous body.As a specific example, in the case of forming the silicone porous bodyhaving a thickness of 0.1 to 1000 μm, the coating amount of thepulverized product relative to the base is, for example, in the rangefrom 0.01 to 60000 μg, 0.1 to 5000 μg, or 1 to 50 μg per square meter ofthe base. Although it is difficult to uniquely define a preferablecoating amount of the sol particle liquid because it depends on theconcentration of a liquid, the coating method, or the like, for example,it is preferable that a coating layer is as thin as possible inconsideration of productivity. When the coating amount is too much, forexample, there is a high possibility that a solvent is dried in a dryingoven before volatilizing. When the solvent is dried before forming thevoid-provided structure by the settlement and deposition of the nanopulverized sol particles in the solvent, there is a possibility thatformation of void spaces is inhibited and the proportion of void spacedecreases. On the other hand, when the coating amount is too little,there is a possibility of increasing the risk of causing coating cissingdue to unevenness of a base, variations in hydrophilicity andhydrophobicity, and the like.

Furthermore, the production method of the present invention includes astep of drying the liquid containing the microporous particles(precursor of porous body (coating film)) as described above. The dryingtreatment is aimed not only for removing the solvent (solvent containedin the sol particle liquid) from the precursor of the porous body butalso for causing the settlement and deposition of the sol particles toform a void-provided structure in the drying treatment, for example. Thetemperature for the drying treatment is, for example, in the range from50° C. to 250° C., 60° C. to 150° C., or 70° C. to 130° C., and the timefor the drying treatment is, for example, in the range from 0.1 to 30minutes, 0.2 to 10 minutes, or 0.3 to 3 minutes. Regarding thetemperature and time for the drying treatment in relation to continuousproductivity and high porosity expression, the lower the better and theshorter the better, for example. When the condition is too strict, thereis a possibility of causing the following problems, for example. Thatis, when the base is a resin film, for example, the base extends in adrying oven as the temperature approaches the glass-transitiontemperature of the base, which causes defects such as cracks in a formedvoid-provided structure right after coating. On the other hand, when thecondition is too mild, there is a possibility of causing the followingproblems, for example. That is, since the film contains a residualsolvent when it comes out of the drying oven, defects in appearance suchas scratches are caused when the film rubs against a roller in the nextstep.

The drying treatment may be, for example, natural drying, drying byheating, or drying under reduced pressure. The drying method is notlimited to particular methods, and a common heating unit can be used,for example. Examples of the heating unit include a hot air fan, aheating roll, and a far-infrared heater. Among them, in view ofperforming continuous production industrially, drying by heating ispreferable. The solvent to be used is preferably a solvent having a lowsurface tension in view of reducing the shrinkage stress in accordancewith the solvent volatilization in drying and reducing the crackphenomenon of the void-provided layer (the silicone porous body) due tothe shrinkage stress. The solvent can be, for example, lower alcoholtypified by isopropyl alcohol (IPA), hexane, perfluorohexane, and thelike. The solvent, however, is not limited thereto.

The drying treatment may be, for example, natural drying, drying byheating, or drying under reduced pressure. The drying method is notlimited to particular methods, and a common heating unit can be used,for example. Examples of the heating unit include a hot air fan, aheating roll, and a far-infrared heater. Among them, in view ofperforming continuous production industrially, drying by heating ispreferable. The solvent to be used is preferably a solvent having a lowsurface tension in view of reducing the shrinkage stress in accordancewith the solvent volatilization in drying and reducing the crackphenomenon of the void-provided layer (the silicone porous body) due tothe shrinkage stress. The solvent can be, for example, lower alcoholtypified by isopropyl alcohol (IPA), hexane, perfluorohexane, and thelike. The solvent, however, is not limited thereto. The surface tensionmay be reduced by adding a small amount of a perfluoro surfactant or asmall amount of a silicon surfactant to the IPA and the like.

According to the production method of the present invention, thethree-dimensional structure of the pulverized product in the precursorof the porous body is immobilized, for example. In the case ofimmobilizing the three-dimensional structure by conventional sintering,for example, the dehydration condensation of a silanol group and theformation of a siloxane bond are induced by high temperature treatmentat 200° C. or more. In the present invention, for example, when a baseis a resin film, the void-provided structure can be formed andimmobilized continuously at about 100° C. which is relatively low forless than several minutes which is short without damaging the base bycausing various additives, which catalyze the dehydration condensationreaction, to react.

The method of chemically bonding the particles is not limited toparticular methods, and can be determined appropriately according to thetype of the gelled silicon compound, for example. Specifically, forexample, the chemical bond can be a chemical crosslinking bond among thepulverized products. Besides this, for example, when inorganic particlessuch as titanium oxide particles are added to the pulverized products,the inorganic particles and the pulverized products can be chemicallybonded by crosslinking. Furthermore, there are a case of using abiocatalyst such as an enzyme and a case of chemically crosslinking thepulverized product and a catalyst at a site which is different from acatalytic activity site. Thus, the present invention can be applied notonly to a void-provided layer (silicone porous body) formed of the solparticles but also to an organic-inorganic hybrid void-provided layer, ahost-guest void-provided layer, and the like, for example. The presentinvention, however, is not limited thereto.

The bonding can be carried out by a chemical reaction of chemicallybonding the pulverized products (microporous particles) in the presenceof a catalyst according to the type of the pulverized product of thegelled compound, for example. The catalyst may be a catalyst forpromoting the crosslinking bond among microporous particles, forexample. The chemical reaction in the present invention is preferably areaction utilizing a dehydration condensation reaction of a residualsilanol group contained in a silica sol molecule. By promoting thereaction between the hydroxyl groups of the silanol group by thecatalyst, the continuous formation of a film in which the void-providedstructure is cured in a short time can be performed. Examples of thecatalyst include: base catalysts such as potassium hydroxide, sodiumhydroxide, and ammonium hydroxide; and acid catalysts such as ahydrochloric acid, an acetic acid, and an oxalic acid. The catalyst,however, is not limited thereto. The catalyst used in the dehydrationcondensation reaction is preferably a base catalyst. Furthermore,photoacid generation catalysts, photobase generation catalysts,photoacid generators, photobase generators, and the like, each of whichexpresses a catalytic activity by light (for example, ultraviolet)irradiation, may preferably be used. The photoacid generation catalysts,photobase generation catalysts, photoacid generators, and photobasegenerators are not limited to particular catalysts, and can be, forexample, as described above. The catalyst can be added to the liquidcontaining the microporous particles (for example, suspension of thepulverized products (microporous particles)), for example, in the stepof preparing the liquid as described above. More specifically, thecatalyst is used by adding it to a sol particle liquid (for example,suspension) containing the pulverized products (microporous particles)right before the coating or the catalyst is used as a mixture by mixingit with a solvent, for example. The mixture may be, for example, acoating liquid obtained by adding the catalyst directly to the solparticle liquid, a solution obtained by dissolving the catalyst in asolvent, or a dispersion liquid obtained by dispersing the catalyst intoa solvent. The solvent is not limited to particular solvents asdescribed above, and examples thereof include water, and buffersolutions.

It is not particularly limited at which stage the chemical reaction inthe presence of the catalyst is performed (caused) in the productionmethod of the present invention. The chemical reaction can be performed,for example, by heating the coating film containing the catalystpreliminarily added to the sol particle liquid (for example, suspension)or irradiating the coating film containing the catalyst preliminarilyadded to the sol particle liquid with light, by heating the coating filmor irradiating the coating film with light after the catalyst has beensprayed to the coating film, or by heating the coating film orirradiating the coating film with light while spraying the catalyst tothe coating film. For example, when the catalyst is a photoactivecatalyst, the ultra-low refractive index layer can be formed bychemically bonding the microporous particles by light irradiation. Whenthe catalyst is a thermoactive catalyst, the ultra-low refractive indexlayer can be formed by chemically bonding the microporous particles byheating. The accumulated light amount in the light irradiation is notlimited to particular values, and is, for example, in the range from 200to 800 mJ/cm², 250 to 600 mJ/cm², or 300 to 400 mJ/cm² in terms of thewave length at 360 nm. From the view point of preventing the effect frombeing insufficient due to the delay of decomposition of the catalystgenerator by light absorption because of insufficient irradiationamount, the accumulated light amount is preferably 200 mJ/cm² or more.From the view point of preventing heat wrinkles from generating due tothe damage on a base below a void-provided layer, the accumulated lightamount is preferably 800 mJ/cm² or less. The conditions for the heattreatment are not limited to particular conditions. The heatingtemperature is, for example, 50° C. to 250° C., 60° C. to 150° C., or70° C. to 130° C., the heating time is, for example, 0.1 to 30 minutes,0.2 to 10 minutes, or 0.3 to 3 minutes. The step of drying the solparticle liquid (for example, suspension) may also serve as a step ofperforming a chemical reaction in the presence of the catalyst. That is,in the step of drying the sol particle liquid (for example, suspension),the pulverized products (microporous particles) may be chemically bondedin the presence of the catalyst. In this case, by further heating thecoating film after the drying step, the pulverized products (microporousparticles) may be bonded more firmly. It is presumed that the chemicalreaction in the presence of the catalyst may be caused also in the stepof preparing the liquid (for example, suspension) containing themicroporous particles and the step of coating the resin film with theliquid containing microporous particles. This presumption, however, doesnot limit the present invention by any means. The solvent to be used ispreferably a solvent having a low surface tension in view of reducingthe shrinkage stress in accordance with the solvent volatilization indrying and reducing the crack phenomenon of the void-provided layer dueto the shrinkage stress, for example. The solvent can be, for example,lower alcohol typified by isopropyl alcohol (IPA), hexane,perfluorohexane, or the like. The solvent, however, is not limitedthereto.

In the manner described above, the ultra-low refractive index layer(laminated film roll) of the present invention can be produced. Theproduction method of the present invention, however, is not limitedthereto.

The thus obtained ultra-low refractive index layer (laminated film roll)of the present invention may be subjected to a strength increasing step(hereinafter, also referred to as an “aging step”) of applying thermalaging to increase the strength, for example. For example, when theultra-low refractive index layer of the present invention is stacked ona resin film, the peel strength to the resin film can be increased bythe strength increasing step (aging step). In the strength increasingstep (aging step), for example, the ultra-low refractive index layer ofthe present invention may be heated. The temperature of the aging stepis, for example, 40° C. to 80° C., 50° C. to 70° C., or 55° C. to 65° C.The time for the reaction is, for example, 5 to 30 hours, 7 to 25 hours,or 10 to 20 hours. By setting the heating temperature low in the agingstep, for example, the peel strength can be increased while reducing theshrinkage of the ultra-low refractive index layer, thereby achievingboth a high proportion of void space and strength.

While the phenomenon and mechanism caused in the strength increasingstep (aging step) are unknown, for example, it is considered that thecatalyst contained in the ultra-low refractive index layer of thepresent invention promotes the chemical bond (for example, crosslinkingreaction) among the microporous particles, thereby increasing thestrength. As a specific example, when the microporous particles aresilicon compound microporous particles (for example, pulverized productsof a gelled silica compound) and residual silanol groups (OH groups) arepresent in the ultra-low refractive index layer, it is considered thatthe residual silanol groups are chemically bonded by a crosslinkingreaction. The catalyst contained in the ultra-low refractive index layerof the present invention is not limited to particular catalysts, and canbe, for example, a catalyst used in the bonding step, a basic substancegenerated by the photobase generation catalyst used in the bonding stepby light irradiation, or an acidic substance generated by the photoacidgeneration catalyst used in the bonding step by light irradiation. Thedescription, however, is illustrative and does not limit the presentinvention.

A pressure-sensitive adhesive/adhesive layer may additionally be formedon the ultra-low refractive index layer of the present invention(pressure-sensitive adhesive/adhesive layer forming step). Specifically,for example, the pressure-sensitive adhesive/adhesive layer may beformed by applying a pressure-sensitive adhesive or an adhesive to theultra-low refractive index layer of the present invention. Thepressure-sensitive adhesive/adhesive layer may be formed on theultra-low refractive index layer of the present invention using anadhesive tape in which the pressure-sensitive adhesive/adhesive layer isformed on a base by adhering the pressure-sensitive adhesive/adhesivelayer side of the adhesive tape on the ultra-low refractive index layerof the present invention. In this case, the base of the adhesive tapemay be kept adhered or peeled from the pressure-sensitiveadhesive/adhesive layer. In the present invention, a “pressure-sensitiveadhesive” and a “pressure-sensitive adhesive layer” are used based onthe premise that an adherend is re-peelable, for example. In the presentinvention, an “adhesive” and an “adhesive layer” are used based on thepremise that an adherend is not re-peelable, for example. In the presentinvention, however, the “pressure-sensitive adhesive” and the “adhesive”are not always distinguishable and the “pressure-sensitive adhesivelayer” and the “adhesive layer” are not always distinguishable. In thepresent invention, there is no particular limitation on thepressure-sensitive adhesives or the adhesives for forming thepressure-sensitive adhesive/adhesive layer, and a commonpressure-sensitive adhesive or adhesive can be used, for example.Examples of the pressure-sensitive adhesive and the adhesive includepolymer adhesives such as acrylic adhesives, vinyl alcohol adhesives,silicone adhesives, polyester adhesives, polyurethane adhesives, andpolyether adhesives; and rubber adhesives. Furthermore, thepressure-sensitive adhesive and the adhesive can be an adhesiveincluding a water-soluble crosslinking agent of vinyl alcohol polymersuch as glutaraldehyde, melamine, or an oxalic acid. One type of thepressure-sensitive adhesives and adhesives may be used alone or two ormore types of them may be used in combination (for example, mixing,lamination, and the like). The thickness of the pressure-sensitiveadhesive/adhesive layer is not limited to particular values, and is, forexample, 0.1 to 100 μm, 5 to 50 μm, 10 to 30 μm, or 12 to 25 μm.

Furthermore, an intermediate layer may be formed between the ultra-lowrefractive index layer of the present invention and thepressure-sensitive adhesive/adhesive layer by causing the ultra-lowrefractive index layer of the present invention to react with thepressure-sensitive adhesive/adhesive layer (intermediate layer formingstep). Owing to the intermediate layer, the ultra-low refractive indexlayer of the present invention and the pressure-sensitiveadhesive/adhesive layer are not easily peeled from each other, forexample. While the reason (mechanism) for this is unknown, it ispresumed that the ultra-low refractive index layer of the presentinvention and the pressure-sensitive adhesive/adhesive layer are noteasily peeled from each other owing to the anchoring property (anchoreffect) of the intermediate layer, for example. The anchoring property(anchor effect) is a phenomenon (effect) that the interface between thevoid-provided layer and the intermediate layer is strongly fixed becausethe intermediate layer is entangled in the void-provided layer in thevicinity of the interface. This reason (mechanism), however, is anexample of a presumable reason (mechanism), and does not limit thepresent invention. The reaction between the ultra-low refractive indexlayer of the present invention and the pressure-sensitiveadhesive/adhesive layer is not limited to particular reactions, and canbe, for example, a reaction by catalysis. The catalyst may be a catalystcontained in the ultra-low refractive index layer of the presentinvention, for example. Specifically, the catalyst can be, for example,a catalyst used in the bonding step, a basic substance generated by thephotobase generation catalyst used in the bonding step by lightirradiation, or an acidic substance generated by the photoacidgeneration catalyst used in the bonding step by light irradiation. Thereaction between the ultra-low refractive index layer of the presentinvention and the pressure-sensitive adhesive/adhesive layer may be, forexample, a reaction (for example, crosslinking reaction) that generatesa new chemical bond. The temperature of the reaction is, for example,40° C. to 80° C., 50° C. to 70° C., or 55° C. to 65° C. The time for thereaction is, for example, 5 to 30 hours, 7 to 25 hours, or 10 to 20hours. This intermediate layer forming step may also serve as thestrength increasing step (aging step) of increasing the strength of theultra-low refractive index layer of the present invention.

The thus obtained ultra-low refractive index layer of the presentinvention may further be stacked on another film (layer) to form alaminate having the porous structure, for example. In this case, thecomponents of the laminate may be stacked through a pressure-sensitiveadhesive or an adhesive, for example.

The components may be laminated by continuous treatment (so called Rollto Roll) using a long film, for example, in terms of efficiency. Whenthe base is a molded product, an element, or the like, the base that hasbeen subjected to a batch process may be laminated.

The method of forming an ultra-low refractive index layer of the presentinvention on a base is described below with reference to a continuoustreatment process using FIGS. 1 to 3 as an example. FIG. 2 shows a stepof adhering a protective film to a formed silicone porous body(ultra-low refractive index layer) and winding the laminate. In the caseof forming the silicone porous body on another functional film, theaforementioned method may be adopted or the formed silicone porous body(ultra-low refractive index layer) may be adhered to another functionalfilm that has been coated and dried, right before winding. The method offorming a film shown in FIG. 2 is an example, and the present inventionis not limited thereto.

The base may be the resin film described in the description as to theultra-low refractive index layer of the present invention. In this case,the ultra-low refractive index layer of the present invention can beobtained by forming the ultra-low refractive index layer on the base.The ultra-low refractive index layer of the present invention can beobtained also by forming the ultra-low refractive index layer on thebase and then stacking the ultra-low refractive index layer on the resinfilm described in the description as to the ultra-low refractive indexlayer of the present invention.

FIG. 1 is a cross sectional view schematically showing an example of theprocess of forming the ultra-low refractive index layer on the base. InFIG. 1, the method of forming an ultra-low refractive index layerincludes: (1) a coating step of coating a base 10 with a sol particleliquid 20″ containing pulverized products of a gelled compound; (2) acoating film forming step (drying step) of drying the sol particleliquid 20″ to form a coating film 20′ which is the precursor layer ofthe ultra-low refractive index layer; and (3) a chemical treatment step(for example, a crosslinking treatment step) of applying chemicaltreatment (for example, crosslinking treatment) to the coating film 20′to form an ultra-low refractive index layer 20. In this manner, as shownin FIG. 1, the ultra-low refractive index layer 20 can be formed on thebase 10. The method of forming an ultra-low refractive index layer mayinclude steps other than the steps (1) to (3) appropriately.

In the coating step (1), the method of coating the base with the solparticle liquid 20″ is not limited to particular methods, and a commonmethod can be adopted. Examples of the method include a slot die method,a reverse gravure coating method, a micro-gravure method (micro-gravurecoating method), a dip method (dip coating method), a spin coatingmethod, a brush coating method, a roller coating method, a flexography,a wire-bar coating method, a spray coating method, an extrusion coatingmethod, a curtain coating method, and a reverse coating method. Amongthem, from the viewpoint of productivity, smoothness of a coating film,and the like, an extrusion coating method, a curtain coating method, aroller coating method, a micro-gravure coating method, and the like arepreferable. The coating amount of the sol particle liquid 20″ is notlimited to particular values, and can be determined appropriately so asto obtain an ultra-low refractive index layer 20 having an appropriatethickness, for example. The thickness of the ultra-low refractive indexlayer 20 is not limited to particular values, and is, for example, asdescribed above.

In the (2) drying step, the sol particle liquid 20″ is dried (i.e.,dispersion medium contained in sol particle liquid 20″ is removed) toform a coating film (precursor layer) 20′. There is no particularlimitation on the condition for the drying treatment, and is asdescribed above.

In the (3) chemical treatment step, the coating film 20′ containing thecatalyst (for example, photoactive catalyst or thermoactive catalystsuch as KOH) which has been added before coating is irradiated withlight or heated to chemically bond (for example, crosslink) thepulverized products in the coating film 20′, thereby forming anultra-low refractive index layer 20. The conditions for the lightirradiation and heating in the (3) chemical treatment step are notlimited to particular conditions, and are as described above. By usingthe resin film as the base 10, the ultra-low refractive index layer 20can be stacked directly on the resin film (base 10), for example.

FIG. 2 schematically shows an example of a slot die coating apparatusand an example of the method of forming an ultra-low refractive indexlayer using the same. Although FIG. 2 is a cross sectional view,hatching is omitted for viewability.

As shown in FIG. 2, the steps of the method using this apparatus arecarried out while carrying a base 10 in one direction by rollers. Thecarrying speed is not limited to particular values, and is, for example,in the range from 1 to 100 m/min, 3 to 50 m/min, or 5 to 30 m/min.

First, the base 10 is delivered from a delivery roller 101 and carriedto a coating roller 102, and the (1) coating step of coating the base 10with a sol particle liquid 20″ is carried out using the coating roller102. Subsequently, the (2) drying step is carried out in an oven zone110. In the coating apparatus shown in FIG. 2, a predrying step iscarried out after the (1) coating step and before the (2) drying step.The predrying step can be carried out at room temperature withoutheating. In the (2) drying step, a heating unit 111 is used. As theheating unit 111, as described above, a hot air fan, a heating roll, afar-infrared heater, or the like can be used appropriately. For example,the (2) drying step may be divided into multiple steps, and the dryingtemperature may be set higher as coming to later steps.

The (3) chemical treatment step is carried out in a chemical treatmentzone 120 after the (2) drying step. In the (3) chemical treatment step,for example, when the coating film 20′ after drying contains aphotoactive catalyst, light is emitted from lamps (light irradiationunits) 121 disposed above and below the base 10. On the other hand, forexample, when the coating film 20′ after drying contains a thermoactivecatalyst, the base 10 is heated using hot air fans 121 disposed aboveand below the base 10 instead of using the lamps (light irradiationdevices) 121. By this crosslinking treatment, the pulverized products inthe coating film 20′ are chemically bonded, and the ultra-low refractiveindex layer 20 is cured and strengthened. Note that, although the (3)chemical treatment step is performed after the (2) drying step in thepresent example, as described above, there is no particular limitationat which stage in the production method of the present invention thechemical bond among the pulverized products is caused. For example, asdescribed above, the (2) drying step may also serve as the (3) chemicaltreatment step. Even when the chemical bond is caused in the (2) dryingstep, the (3) chemical treatment step may be performed to make thechemical bond among the pulverized products firmer.

Furthermore, in the steps (for example, predrying step, the (1) coatingstep, step of preparing a coating liquid (for example, suspension), andthe like) before the (2) drying step, the chemical bond among thepulverized products may be caused. After the (3) chemical treatmentstep, a laminate in which the ultra-low refractive index layer 20 isformed on the base 10 is wound by a winding roller 105. By using theresin film as the base 10, for example, the ultra-low refractive indexlayer 20 may be directly formed on the resin film (base 10). In FIG. 2,the ultra-low refractive index layer 20, which is a laminate, isprotected by coating with a protecting sheet delivered from a roller106. Instead of the protecting sheet, another layer formed of a longfilm may be formed on the ultra-low refractive index layer 20.

FIG. 3 schematically shows an example of a micro-gravure coatingapparatus and an example of the method of forming an ultra-lowrefractive index layer using the same. Although FIG. 3 is a crosssectional view, hatching is omitted for viewability.

As shown in FIG. 3, the steps of the method using this apparatus arecarried out while carrying the base 10 in one direction by rollers as inFIG. 2. The carrying speed is not limited to particular values, and is,for example, in the range from 1 to 100 m/min, 3 to 50 m/min, or 5 to 30m/min.

First, the (1) coating step of coating the base 10 with a sol particleliquid 20″ is carried out while carrying the base 10 delivered from adelivery roller 201. As shown in FIG. 3, the coating with the solparticle liquid 20″ is performed using a liquid reservoir 202, a doctor(doctor knife) 203, and a micro-gravure 204. Specifically, the solparticle liquid 20′ in the liquid reservoir 202 is applied to thesurface of the micro-gravure 204 and the coating of the surface of thebase 10 is performed using the micro-gravure 204 while controlling thethickness to a predetermined thickness using a doctor 203. Themicro-gravure 204 is merely illustrative. The present invention is notlimited thereto, and any other coating unit may be adopted.

Subsequently, the (2) drying step is performed. Specifically, as shownin FIG. 3, the base 10 coated with the sol particle liquid 20″ iscarried into an oven zone 210 and the sol particle liquid 20″ is driedby heating using heating units 211 disposed in the oven zone 210. Theheating units 211 can be, for example, the same as those shown in FIG.2. For example, the (2) drying step may be divided into multiple stepsby dividing the oven zone 210 into multiple sections, and the dryingtemperature may be set higher as coming to later steps. The (3) chemicaltreatment step is carried out in a chemical treatment zone 220 after the(2) drying step. In the (3) chemical treatment step, for example, whenthe coating film 20′ after drying contains a photoactive catalyst, lightis emitted from lamps (light irradiation units) 221 disposed above andbelow the base 10. On the other hand, for example, when the coating film20′ after drying contains a thermoactive catalyst, the base 10 is heatedusing hot air fans (heating units) 221 disposed below the base 10instead of using lamps (light irradiation devices) 221. By thiscrosslinking treatment, the pulverized products in the coating film 20′are chemically bonded, and the ultra-low refractive index layer 20 isformed.

After the (3) chemical treatment step, a laminate in which the porousstructure 20 is formed on the base 10 is wound by a winding roller 251.By using the resin film as the base 10, the ultra-low refractive indexlayer 20 can be stacked directly on the resin film (base 10), forexample. Thereafter, for example, another layer may be formed on thelaminate. Furthermore, another layer may be stacked on the laminatebefore winding the laminate by the winding roller 251, for example.

FIGS. 4 to 6 show another example of a continuous treatment process offorming an ultra-low refractive index layer of the present invention. Asshown in the cross sectional view of FIG. 4, this method is the same asthe method shown in FIGS. 1 to 3 except that (4) strength increasingstep (aging step) is carried out after the (3) chemical treatment step(for example, crosslinking treatment step) of forming an ultra-lowrefractive index layer 20. As shown in FIG. 4, the strength of theultra-low refractive index layer 20 is increased in the (4) strengthincreasing step (aging step), thereby forming an ultra-low refractiveindex layer 21 with a greater strength. There is no particularlimitation on the (4) strength increasing step (aging step), and can be,for example, as described above.

FIG. 5 is a schematic view showing an example of a slot die coatingapparatus and an example of the method of forming an ultra-lowrefractive index layer using the same, which are different from thoseshown in FIG. 2. As can be seen, the coating apparatus shown in FIG. 5is the same as the apparatus shown in FIG. 2 except that the apparatusshown in FIG. 5 includes a strength increasing zone (aging zone) 130where the (4) strength increasing step (aging step) is carried out rightnext to the chemical treatment zone 120 where the (3) chemical treatmentstep is carried out. That is, after the (3) chemical treatment step, the(4) strength increasing step (aging step) is carried out in the strengthincreasing zone (aging zone) 130 to increase the peel strength of theultra-low refractive index layer 20 relative to a resin film 10, therebyforming an ultra-low refractive index layer 21 having a higher peelstrength. The (4) strength increasing step (aging step) may be carriedout by heating the ultra-low refractive index layer 20 in the samemanner as described above using hot air fans (heating units) 131disposed above and below the base 10, for example. The conditionsincluding the heating temperature, the time, and the like are notlimited to particular values, and can be, for example, as describedabove. After the (4) strength increasing step, similar to the processshown in FIG. 3, a laminated film in which the ultra-low refractiveindex layer 21 is formed on the base 10 is wound by a winding roller105.

FIG. 6 is a schematic view showing an example of a micro-gravure coatingapparatus and an example of the method of forming a porous structureusing the same, which are different from those shown in FIG. 3. As canbe seen, the coating apparatus shown in FIG. 6 is the same as theapparatus shown in FIG. 3 except that the apparatus shown in FIG. 6includes a strength increasing zone (aging zone) 230 where the (4)strength increasing step (aging step) is carried out right next to thechemical treatment zone 220 where the (3) chemical treatment step iscarried out. That is, after the (3) chemical treatment step, the (4)strength increasing step (aging step) is carried out in the strengthincreasing zone (aging zone) 230 to increase the peel strength of theultra-low refractive index layer 20 relative to a resin film 10, therebyforming an ultra-low refractive index layer 21 having a higher peelstrength. The (4) strength increasing step (aging step) may be carriedout by heating the ultra-low refractive index layer 20 in the samemanner as described above using hot air fans (heating units) 231disposed above and below the base 10, for example. The conditionsincluding the heating temperature, the time, and the like are notlimited to particular values, and can be, for example, as describedabove. After the (4) strength increasing step, similar to the processshown in FIG. 3, a laminated film in which the ultra-low refractiveindex layer 21 is formed on the base 10 is wound by a winding roller251.

FIGS. 7 to 9 show another example of a continuous treatment process offorming an ultra-low refractive index layer of the present invention. Asshown in the cross sectional view of FIG. 7, this method includes, afterthe (3) chemical treatment step (for example, crosslinking treatmentstep) of forming an ultra-low refractive index layer 20, (4)pressure-sensitive adhesive/adhesive layer applying step(pressure-sensitive adhesive/adhesive layer forming step) of coating theultra-low refractive index layer 20 with pressure-sensitiveadhesive/adhesive layer 30 and (5) intermediate layer forming step ofcausing the ultra-low refractive index layer 20 to react with thepressure-sensitive adhesive/adhesive layer 30 to form an intermediatelayer 22. Except for these, the method shown in FIGS. 7 to 9 is the sameas the method shown in FIGS. 4 to 6. In, FIG. 7, the (5) intermediatelayer forming step also serves as a step of increasing the strength ofthe ultra-low refractive index layer 20 (strength increasing step) sothat the ultra-low refractive index layer 20 changes to an ultra-lowrefractive index layer 21 having a higher strength after the (5)intermediate layer forming step. The present invention, however, is notlimited thereto, and the ultra-low refractive index layer 20 may notchange after the (5) intermediate layer forming step, for example. The(4) pressure-sensitive adhesive/adhesive layer applying step(pressure-sensitive adhesive/adhesive layer forming step) and the (5)intermediate layer forming step are not particularly limited, and canbe, for example, as described above.

FIG. 8 is a schematic view showing another example of a slot die coatingapparatus and another example of the method of forming an ultra-lowrefractive index layer using the same. As can be seen, the coatingapparatus shown in FIG. 8 is the same as the apparatus shown in FIG. 5except that the apparatus shown in FIG. 8 includes a pressure-sensitiveadhesive/adhesive layer applying zone 130 a where the (4)pressure-sensitive adhesive/adhesive layer applying step is carried outright next to the chemical treatment zone 120 where the (3) chemicaltreatment step is carried out. In FIG. 8, the same heat treatment asthat carried out in the strength increasing zone (aging zone) 130 ofFIG. 5 can be carried out in an intermediate layer forming zone (agingzone) 130 disposed right next to the pressure-sensitiveadhesive/adhesive layer applying zone 130 a using hot air fans (heatingunits) 131 disposed above and below the base 10. That is, the apparatusshown in FIG. 8 carries out, after the (3) chemical treatment step, the(4) pressure-sensitive adhesive/adhesive layer applying step(pressure-sensitive adhesive/adhesive layer forming step) of applying apressure-sensitive adhesive or an adhesive to the ultra-low refractiveindex layer 20 to form a pressure-sensitive adhesive/adhesive layer 30in the pressure-sensitive adhesive/adhesive layer applying zone 130 ausing pressure-sensitive adhesive/adhesive layer applying units 131 a.Instead of applying the pressure-sensitive adhesive or the adhesive, forexample, an adhesive tape including the pressure-sensitiveadhesive/adhesive layer 30 may be adhered (taped) as described above.Thereafter, the (5) intermediate layer forming step (aging step) iscarried out in the intermediate layer forming zone (aging zone) 130 tocause the ultra-low refractive index layer 20 to react with thepressure-sensitive adhesive/adhesive layer 30, thereby forming anintermediate layer 22. In this step, the ultra-low refractive indexlayer 20 changes to an ultra-low refractive index layer 21 having ahigher strength as described above. The conditions of the hot air fans(heating units) 131 including the heating temperature, the time, and thelike are not limited to particular values, and can be, for example, asdescribed above.

FIG. 9 is a schematic view showing another example of a micro-gravurecoating apparatus and another example of the method of forming a porousstructure using the same. As can be seen, the coating apparatus shown inFIG. 9 is the same as the apparatus shown in FIG. 6 except that theapparatus shown in FIG. 9 includes a pressure-sensitiveadhesive/adhesive layer applying zone 230 a where the (4)pressure-sensitive adhesive/adhesive layer applying step is carried outright next to the chemical treatment zone 220 where the (3) chemicaltreatment step is carried out. In FIG. 9, the same heat treatment asthat carried out in the strength increasing zone (aging zone) 230 ofFIG. 6 can be carried out in an intermediate layer forming zone (agingzone) 230 disposed right next to the pressure-sensitiveadhesive/adhesive layer applying zone 230 a using hot air fans (heatingunits) 231 disposed above and below the base 10. That is, the apparatusshown in FIG. 9 carries out, after the (3) chemical treatment step, the(4) pressure-sensitive adhesive/adhesive layer applying step(pressure-sensitive adhesive/adhesive layer forming step) of applying apressure-sensitive adhesive or an adhesive to the ultra-low refractiveindex layer 20 to form a pressure-sensitive adhesive/adhesive layer 30in the pressure-sensitive adhesive/adhesive layer applying zone 230 ausing pressure-sensitive adhesive/adhesive layer applying units 231 a.Instead of applying the pressure-sensitive adhesive or the adhesive, forexample, an adhesive tape including the pressure-sensitiveadhesive/adhesive layer 30 may be adhered (taped) as described above.Thereafter, the (5) intermediate layer forming step (aging step) iscarried out in the intermediate layer forming zone (aging zone) 230 tocause the ultra-low refractive index layer 20 to react with thepressure-sensitive adhesive/adhesive layer 30, thereby forming anintermediate layer 22. In this step, the ultra-low refractive indexlayer 20 changes to an ultra-low refractive index layer 21 having ahigher strength as described above. The conditions of the hot air fans(heating units) 231 including the heating temperature, the time, and thelike are not limited to particular values, and can be, for example, asdescribed above.

[3. Optical Element]

The optical element of the present invention is characterized in that itincludes the ultra-low refractive index layer of the present inventionas described above. The optical element of the present invention ischaracterized in that it includes the ultra-low refractive index layerof the present invention, and other configurations are by no meanslimited. The optical element of the present invention may furtherinclude another layer besides the ultra-low refractive index layer ofthe present invention, for example.

Furthermore, the optical element of the present invention ischaracterized in that it includes the ultra-low refractive index layerof the present invention as a low reflective layer. The optical elementof the present invention is characterized in that it includes the lowreflective layer of the present invention, and other configurations areby no means limited. The optical element of the present invention mayfurther include another layer besides the ultra-low refractive indexlayer of the present invention, for example. The optical element of thepresent invention is, for example, in the form of a roll.

EXAMPLES

The examples of the present invention are described below. The presentinvention, however, is not limited by the following examples.

Example 1

In the present example, an ultra-low refractive index layer of thepresent invention was produced as described below.

(1) Gelation of Silicon Compound

0.95 g of MTMS which is the precursor of a silicon compound wasdissolved in 2.2 g of DMSO. 0.5 g of 0.01 mol/L oxalic acid aqueoussolution was added to the mixture, and the resultant was stirred at roomtemperature for 30 minutes to hydrolyze MTMS, thereby preparingtris(hydroxy)methylsilane.

0.38 g of ammonia water having a concentration of 28% and 0.2 g of purewater were added to 5.5 g of DMSO, then the aforementioned mixture thathad been subjected to the hydrolysis treatment was added thereto, andthe resultant was stirred at room temperature for 15 minutes to gelatetris(hydroxy)methylsilane, thereby obtaining a gelled silicon compound.

(2) Aging Treatment

The aging treatment was carried out as follows. The mixture that hadbeen subjected to the gelation treatment was incubated at 40° C. for 20hours.

(3) Pulverizing Treatment

Subsequently, the gelled silicon compound that had been subjected to theaging treatment was granulated into pieces of several millimeters toseveral centimeters using a spatula. 40 g of IPA was added thereto, themixture was stirred lightly and then was allowed to stand still at roomtemperature for 6 hours, and a solvent and a catalyst in the gel weredecanted. This decantation treatment was repeated three times, and thesolvent replacement was completed. Then, the gelled silicon compound inthe mixture was subjected to pulverizing treatment (high pressuremedialess pulverization). This pulverizing treatment (high pressuremedialess pulverization) was carried out using a homogenizer (product ofSMT Corporation, product name: UH-50) as follows. That is, 1.18 g of geland 1.14 g of IPA were added to 5 cc screw bottle and pulverized for 2minutes at 50 W and 20 kHz.

The gelled silicon compound in the mixture was pulverized by thepulverizing treatment, whereby the mixture was changed to a sol particleliquid of the pulverized product. The volume average particle sizeshowing particle size variations of the pulverized products contained inthe mixture measured by a dynamic light scattering nanotrac particlesize analyzer (product of NIKKISO CO., LTD., product name: UPA-EX150)was 0.50 to 0.70. 0.02 g of 0.3 wt % KOH aqueous solution was added to0.5 g of the sol liquid, thereby preparing a coating liquid.

(4) Formation of Coating Film and Silicone Porous Body Roll

The coating liquid was applied to the surface of a resin film (length:100 m) made of polyethylene terephthalate (PET) by bar coating, therebyforming a coating film. 6 μL of the sol liquid was applied to per squaremillimeter of the surface of the base. The coating film was treated at100° C. for one minute, and the formation of the precursor of thesilicone porous body and the crosslinking reaction among the pulverizedproducts in the precursor were completed, thereby obtaining a roll inthe winding step. Thereby, a silicone porous body roll having athickness of 1 μm in which the pulverized products are chemically bondedwas formed on the base.

(5) Measurement of Property of Ultra-Low Refractive Index Layer

As to the porous body formed on the base, the refractive index, thehaze, the strength (abrasion resistance measured with BEMCOT®), and thepore size were measured according to the aforementioned method.

Example 2

A silicone porous body was formed in the same manner as in Example 1except that the amount of ammonia water, which is a catalyst, wasreduced to 0.09 g in gelation of silicon compound precursor MTMS, whichis a raw material and the conditions for the incubation in the agingstep were changed from at 40° C. for 20 hours to at room temperature for2 hours. Then, the properties of the silicone porous body were measured.

Comparative Example 1

A porous body was formed in the same manner as in Comparative Example 1except that KOH was not added to the coating liquid. Then, theproperties of the silicone porous body were measured.

The results are summarized in the following Table 1.

TABLE 1 Item Example 1 Example 2 Comparative Example 1 Refractive index1.10 1.24 1.31 Haze 0.3 0.4 0.4 Abrasion resistance 65% 89% 9% Rollappearance No scratch No scratch Many scratches Pore size 6 nm

As summarized in Table 1, the ultra-low refractive index layer having athickness of 1 μm obtained in Example 1 has a refractive index of notmore than 1.3, which is equivalent to the refractive index of an airlayer and is different from the refractive index of the ultra-lowrefractive index layer obtained in Comparative Example 1. The bondingtreatment reduced scratches from being caused in winding of the roll,which allowed a long film with favorable roll appearance to be obtained.These results also show that each of the ultra-low refractive indexlayers obtained in Examples 1 and 2, despite its porous structure withvoid space, has a sufficient strength and sufficient transparency.

Example 3

In the present example, an ultra-low refractive index layer of thepresent invention was produced as described below.

The “(1) gelation of silicon compound” and the “(2) aging treatment”were carried out in the same manner as in Example 1. Subsequently, the“(3) pulverizing treatment” was carried out in the same manner as inExample 1 except that an isopropyl alcohol (IPA) solution containing 1.5wt % photobase generation catalyst (product of Wako Pure ChemicalIndustries, Ltd., product name: WPBG 266) instead of 0.3 wt % KOHaqueous solution was added to the sol particle liquid, thereby preparinga coating liquid. The amount of the IPA solution containing thephotobase generation catalyst to be added relative to 0.75 g of the solparticle liquid was 0.031 g. Then, the “(4) formation of coating filmand formation of silicone porous body roll” were carried out in the samemanner as in Example 1. The porous body obtained in this manner afterdrying was irradiated with UV. The condition for the UV irradiation wasas follows. That is, the wavelength of the light was 360 nm and theamount of the light irradiation (energy) was 500 mJ. After UVirradiation, thermal aging at 60° C. was carried out for 22 hours,thereby forming an ultra-low refractive index layer (silicone porousbody roll) of the present example.

Example 4

An ultra-low refractive index layer of the present example was producedin the same manner as in Example 2 except that thermal aging was notperformed after UV irradiation.

Example 5

An ultra-low refractive index layer of the present example was producedin the same manner as in Example 2 except that, after the IPA solutioncontaining the photobase generation catalyst had been added, 0.018 g of5 wt % bis(trimethoxy)silane was added to 0.75 g of the sol liquid toadjust a coating liquid.

Example 6

An ultra-low refractive index layer of the present example was producedin the same manner as in Example 2 except that the amount of the IPAsolution containing the photobase generation catalyst to be addedrelative to 0.75 g of sol liquid was 0.054 g.

Example 7

After subjecting the porous body after drying to the UV irradiation inthe same manner as in Example 2 and before subjecting the porous body tothe thermal aging, the pressure-sensitive adhesive side of a PET film,to one side of which a pressure-sensitive adhesive (pressure-sensitiveadhesive/adhesive layer) is applied, was adhered to the porous body atroom temperature, and then the porous body was subjected to thermalaging at 60° C. for 22 hours. Except for this, an ultra-low refractiveindex layer of the present example was produced in the same manner as inExample 2.

Example 8

An ultra-low refractive index layer of the present example was producedin the same manner as in Example 6 except that thermal aging was notcarried out after adhering the PET film.

Example 9

An ultra-low refractive index layer of the present example was producedin the same manner as in Example 6 except that, after the IPA solutioncontaining the photobase generation catalyst had been added, 0.018 g of5 wt % bis(trimethoxy)silane was added to 0.75 g of the sol liquid toadjust a coating liquid.

Example 10

An ultra-low refractive index layer of the present example was producedin the same manner as in Example 6 except that the amount of the IPAsolution containing the photobase generation catalyst to be addedrelative to 0.75 g of the sol liquid was 0.054 g.

The refractive index, the peel strength, and the haze of each of theultra-low refractive index layers obtained in Examples 3 to 10 weremeasured according to the above-described method. The results aresummarized in Tables 2 and 3. In measurement of the peel strength ofeach of the ultra-low refractive index layers obtained in Examples 7 to10, since a PET film and a pressure-sensitive adhesive had alreadyadhered to the laminated film roll, adhering the PET film and acrylicpressure-sensitive adhesive to the laminated film roll was omitted.

TABLE 2 Example 3 Example 4 Example 5 Example 6 Refractive 1.14 1.151.15 1.16 index Peel strength 2N/25 mm 1.2N/25 mm 3N/25 mm 2N/25 mm Haze0.4  0.4  0.4  0.4  Abrasion 70% 70% 75% 78% resistance Roll No scratchNo scratch No scratch No scratch appearance

TABLE 3 Example 7 Example 8 Example 9 Example 10 Refractive 1.14 1.151.15 1.16 index Peel strength 2N/25 mm 1.2N/25 mm 3N/25 mm 2N/25 mm Haze0.4  0.4  0.4  0.4  Abrasion 70% 75% 75% 78% resistance Roll No scratchNo scratch No scratch No scratch appearance

As summarized in Tables 2 and 3, each of the ultra-low refractive indexlayers having a thickness of 1 μm obtained in Examples 3 to 10 has avery low refractive index in the range from 1.14 to 1.16. Furthermore,these ultra-low refractive index layers each show a very low haze valueof 0.4, which shows very high transparency. Furthermore, since each ofthe ultra-low refractive index layers obtained in Examples 3 to 10 has ahigh peel strength, even after forming a roll by winding the ultra-lowrefractive index layer, the layer is less likely to be peeled fromanother layer of the laminated film roll. Moreover, each of theultra-low refractive index layers obtained in Examples 3 to 10 issuperior in an abrasion resistance and is hardly scratched. Each of thecoating liquids of Examples 3 to 10 was visually observed after one weekstorage, and no change was observed. This shows that the coating liquidis superior in the storage stability and that a laminated film roll ofstable quality can be produced efficiently.

INDUSTRIAL APPLICABILITY

As described above, the ultra-low refractive index layer of the presentinvention showing the above-described properties easily achieves a lowrefractive index, which allows the ultra-low refractive index layer tobe a substitute for an air layer, for example. Thus, there is no need toprovide air layers by disposing components at regular spacings forachieving a low refractive index. By disposing the ultra-low refractiveindex layer of the present invention at a desired site, a low refractionindex can be achieved. Thus, the ultra-low refractive index layer of thepresent invention is useful to an optical element which requires a lowrefractive index, for example.

EXPLANATION OF REFERENCE NUMERALS

-   10 base-   20 ultra-low refractive index layer-   20′ coating film (precursor layer)-   20″ sol particle liquid-   21 ultra-low refractive index layer with improved strength-   101 delivery roller-   102 coating roller-   110 oven zone-   111 hot air fan (heating unit)-   120 chemical treatment zone-   121 lamp (light irradiation unit) or hot air fan (heating unit)-   130 a pressure-sensitive adhesive/adhesive layer applying zone-   130 intermediate forming zone-   131 a pressure-sensitive adhesive/adhesive layer applying unit-   131 hot air fan (heating unit)-   105 winding roller-   106 roller-   201 delivery roller-   202 liquid reservoir-   203 doctor (doctor knife)′-   204 micro-gravure-   210 oven zone-   211 heating unit-   220 chemical treatment zone-   221 lamp (light irradiation unit) or hot air fan (heating unit)-   230 a pressure-sensitive adhesive/adhesive layer applying zone-   230 intermediate forming zone-   231 a pressure-sensitive adhesive/adhesive layer applying unit-   231 hot air fan (heating unit)-   251 winding roller

The invention claimed is:
 1. A laminated film roll comprising: anultra-low refractive index layer forms a monolithic structure havingminute void spaces, and an open cell structure with multiple poredistributions in which the minute void spaces are aggregated andthree-dimensionally interconnected; and a resin film, wherein theultra-low refractive index layer is stacked on the resin film, theultra-low refractive index layer consists of structural units in theshape of particles which are chemically and directly bonded by acatalyst, and the minute void spaces formed between the structural unitsin the shape of particles, the structural units in the shape ofparticles are microporous inorganic particles of a pulverized product ofa gelled silicon compound, wherein a volume average particle size of themicroporous inorganic particles is more than 0.10 μm, and wherein theultra-low refractive index layer has a proportion of void space of 40%or more, and a refractive index of 1.2 or less.
 2. The laminated filmroll according to claim 1, wherein the bond among the structural unitsincludes a hydrogen bond or a covalent bond.
 3. The laminated film rollaccording to claim 1, wherein the microporous inorganic particle furtherincludes at least one element selected from the group consisting of Mg,Al, Ti, Zn, and Zr.
 4. The laminated film roll according to claim 1,wherein the minute void spaces have a pore size is in a range from 2 to200 nm.
 5. The laminated film roll according to claim 1, wherein theultra-low refractive index layer has a thickness in a range from 0.01 to100 μm.
 6. The laminated film roll according to claim 1, wherein theultra-low refractive index layer has a haze value of less than 5%. 7.The laminated film roll according to claim 1, wherein the volume averageparticle size of the microporous inorganic particles is 0.20 μm or more.8. An optical element comprising: an ultra-low refractive index layerforming a monolithic structure having minute void spaces, and an opencell structure with multiple pore distributions in which the minute voidspaces are aggregated and three-dimensionally interconnected; and aresin film, wherein the ultra-low refractive index layer is stacked onthe resin film, the ultra-low refractive index layer consists ofstructural units in the shape of particles which are chemically anddirectly bonded by a catalyst, and minute void spaces formed between thestructural units in the shape of particles, the structural units in theshape of particles are microporous inorganic particles of a pulverizedproduct of a gelled silicon compound, wherein a volume average particlesize of the microporous inorganic particles is more than 0.10 μm,wherein the ultra-low refractive index layer has a proportion of voidspace of 40% or more, and a reflective index of 1.2 or less, and whereinthe optical element is in the form of a film roll.